Sunday, July 15, 2018 : Anatomy of a Spammy Campaign

Mailinator is a popular disposable email service. It's also become a great tool for QA Teams to test email receipt, acknowledgment, authentication loops, and formatting. But in the beginning (um, wow - 15 years ago? really?) it was a tool to help people avoid spam.

Mailinator gets many millions of emails per day. At peak, it can be thousands of emails per second. Over time it has become ever more efficient at dealing with the deluge; processing, compressing, storing, and analyzing them.  Once someone uses a Mailinator address, they tend to abandon it and use a different one next time. But the Internet never forgets. It seems like every Mailinator address ever used has found its way onto a marketing list somewhere.

Here's a picture of the last 6 days of email entering the system:

Six days of frequent Subjects coming to Mailinator

This graph (click on the image for a bigger version) shows a sub-set of email entering the Mailinator system. Each vertical bar represents a 10 minute interval. For each 10 minute interval, we count emails that have the same subject line that arrived 10 or more times. In each bar, a colored segment represents emails with a single subject line. Blasts of email that come as one-offs aren't on this graph, so this isn't so much a representation of Mailinator's total volume but more a segment of our flow that feels spammy.

Also, we're only selecting from email sent to the Public Mailinator system. Our subscribers get a separate, private (persistent) email system where they can send their test emails. None of those emails are represented here - and they wouldn't be anyway since they're not spam.

Look at that spike of 190k emails on July 4th at 12:40pm in the center of the graph. You also might notice that most of that line is one color (green). That shows the many tens of thousands of emails with the same subject line that Mailinator received in that 10 minute interval.

Consider also the corresponding graph:

Six days of sending IP addresses

This graph shows the IP addresses that sent emails in the same time period. Notice that the spike is still there, but the graphs don't match up. Similarly to the first graph, only IP addresses that sent 10 emails within 10 minutes are on the graph. Except for a few spots, you don't really see the same incidence of colored bands. The IP addresses are far more spread out. The implication here is that many, many IP addresses are responsible for sending the same email to Mailinator. It's not uncommon to see thousands of IP addresses involved in one spam blast.

Even so, you can still see that spike at 7/4/2018 12:40pm. That was a company sending a 'marketing campaign' from one IP address. We won't mention who sent those (what they're doing isn't particularly interesting, and is far from unique), but it's likely that IP address was blacklisted in Gmail and other more discriminating email systems. Clearly, Mailinator isn't particularly discriminating.

Here's a closer look at the top graph:

Spam Campaign at 5am

Here we've zoomed in on the "Top Subject Lines" graph for 7/5/2018 3:10am to 7/5/2018 8:47pm. The first thing we notice is that spammers are prompt! That campaign starts exactly at 5am.

Look at the overlay. From 6:40 to 6:50 we got just over 60,000 emails that fit our spammy profile. There are three spam campaigns listed. The first one is for Michael Kors Bags. Classic Style! 90% off! What a steal! Well, I'm sure they're very nice and convey an exclusive feeling. They sent our system 15,400 exclusive offers in that 10 minute interval.

Next in line looks to be (just guessing) a phishing campaign for people who might happen to have a Netgear router.

The third one is a combination of several subject lines all coming in around 4.4k, 4.5k, and 4.6k (if we mouse-over other intervals the Netgear campaign is all over the place, but this one is consistently 4.5k).

Notice we're highlighted on an email with the subject line "Welcome to our company:" Let's consider a graph that shows all the IP addresses that sent us an email with that subject line in that time interval - and we'll collect them all, not only the ones that sent 10 or more:

One Email - thousands of Sending IPs

So many different colors! Which means that it's a lot of different IP addresses.

Check out the mouseover for that 10 minute interval. For all those emails, the most we got from a single IP address was 3. That's a pretty well distributed spam network! Good job guys.

That email and it's siblings ("New offer", "Good day!", and "Hello!") are all part of the same campaign sent from many thousands of computers. From what we can see, it's being going on for more than a week.

For a while now, Mailinator has used this type of information to better store the emails that people are actually requesting. Remember, Mailinator doesn't have user accounts associated with inboxes.

The public inboxes here don't belong to anyone. The very nature of Mailinator is that inboxes are completely public. A fair characterization of our privacy policy here is: "At Mailinator, there is none!", and this is a good time to remind people that they should never send private information to Mailinator's public system (our FAQ used to say that if you sent super-sensitive private stuff here then you were a stupidhead - but now we're more polite).

[But still, please, don't do it]

We think we can help provide pretty good anonymity in some cases. The public system doesn't really want to know who you are.

Mailinator populates inboxes when email arrives. One way to think about our system is that all inboxes (trillions of them *) already exist, it's just that most aren't currently being used. Many users have found us to be a very handy tool for receiving a one-off email. More and more people are using us for email testing and that's very encouraging.

The sort of analysis we talk about here has helped us make some some useful and interesting architectural choices, and it has informed the way we deal with the enormous volume of email that Mailinator has evolved to receive.

It's also got us thinking - what sort of information lurks in data that flows our way every day? We have tools and a back-end infrastructure that allows a very fine-grained look at a really large volume of spam. Now that we have the ability, we're really excited to dig a little deeper into this pile of potted meat product.

Thanks for using Mailinator and keep sending it spam. It makes our graphs look pretty cool.

* It's actually much more than trillions. We looked at the RFCs, and with 64 characters in the <local-part> of an address, and the weird mix of rules for allowable characters, and even weirder rules for when and where some characters are and aren't allowed, it's a bit convoluted. But with a crayon and the back of an old envelope, we figure that a decent approximation is something like 2.4 x 10^111 inboxes for a domain.

If your crayon is sharper than ours, we'd love to hear your estimate.

Also, Mailinator can handle 212 characters in the <local-part> - which makes the number considerably larger.

You might need two crayons.

Friday, July 28, 2017

Introducing the Mailinator Real-Time Inbox

Mailinator is changing the way email works.

For most users, an inbox is an email’s final destination on a journey through the internet. It’s an endpoint, your endpoint, that holds your emails as they come to you. Checking your email, or refreshing your browser, is when your inbox asks if there’s anything new for you.

But Mailinator doesn’t see it that way because inboxes don’t really belong to anyone. The public Mailinator system gets many (oh so many) millions of emails per day - and you can read any of them. So can anyone else. With Mailinator, you don’t even have to create an inbox. You can just start sending email to it.

One way to think about it is that all inboxes already exist. Another way to think about it is that Mailinator creates inboxes on-the-fly as email arrives.

From Mailinator’s point of view the email flow is relentless and constant. We call it the Mailinator Stream. Previously, inboxes got new mail the way all inboxes do - periodically they asked the server if there was any new email to display.

But now we’ve hooked you up to the stream. Directly. To every inbox. In real time.

Welcome to the Mailinator Real-time Inbox. 

The moment someone sends an email to Mailinator, it’ll show up on your screen (just as fast as the internet allows). There’s no delay. You’ll never again have to hit ‘refresh’ on a Mailinator inbox. (Go ahead and give it at try - pick an inbox, send an email to it, and watch it arrive an instant later - be sure to turn off the "undo" feature of Gmail or it'll delay 30 seconds before sending)

Now, with Mailinator’s inbox page tapped into the stream, an inbox is a filter. Everything that matches your filter will show up in real time.

For most users, that won’t make much of a difference. You’ll get your anonymous, no-sign-up emails like always, except now they'll arrive instantly. An inbox will still act like an inbox.

But paid subscribers with private domains can query the stream at a deeper level. (For those who didn't know, you can upgrade your Mailinator account to get your own private, not-auto-deleting version of Mailinator pointing at at your own domain that your whole team can access simultaneously).

Subscribers can create more complex filters and persistent queries that capture more than just a single <inbox> from the stream. You can tap into multiple inboxes at the same time. You can also use a trailing asterisk as a wildcard. Asking your inbox to capture testing* will fill your inbox with all the emails sent to testing1, and testing99, and testing-xyz, and anything else which matches.

Mailinator has always been about providing public email addresses for anyone to use (no signup required), and now it does it in real-time with some great new features. Interested in your own private Mailinator where every inbox you can think up is yours (instantly and wildcard searchable)? Request a Trial today.

Thanks for using Mailinator!

Thursday, May 4, 2017

Mailinator and the Recent Google Docs Phishing Attack

Yesterday (Wednesday, May 3rd), someone launched a clever phishing attack against Google users.

They wrote a little application and falsely named it "Google Docs." Given the chance, it compromises your Gmail account and reads your contacts list. Then, using Google’s own email servers, it sends itself to all your contacts.

This kind of attack lives or dies by how successful it is at getting people to believe it and click through. If no one clicks, or if no one grants it the permissions it asks for, then it doesn't spread and nothing happens. But every time someone clicks through and grants the app the access it wants, the attack multiplies by the number of times it propagates.

The attack was very successful at getting people to click through and grant it permissions, and it spread very quickly.

But it did so in a quirky way, one that made Mailinator one of its victims. It emailed itself from one victim's account to the next set of targets by BCC (blind carbon-copy). If you received the email, it came to you that way. Your email address wasn't in the TO field, it was in the BCC field.

That's a little bit clever. Since the BCC: is blind, the victim doesn't see themselves included in a long list of recipients (many of whom they don't recognize), which is often a big clue that the email is nefarious (or some dumb joke that a clueless relative has forwarded to everyone they know). Any one attack email might have been BCC'd to dozens of new victims.

When you send an email, you can't just BCC people. To make it legit, there has to be something in the TO field. Since all the victim's contacts were in the BCC field, the address the emails are TO isn't part of the attack. The attacker just needs a dumping ground. Something that looks just-so to the target; not a name that stands out for being unfamiliar, but also a real address that works and won’t bounce. That will improve deliverability and believability. So who did the attacker choose to send these emails to?

What is the significance of that inbox? As far as we can tell, there isn't one. Since all addresses already exist at Mailinator, using your finger to hold down a key for a bit generates a completely innocuous - but usable - inbox name. The significance of using is clear: our well-deserved reputation for successfully handling high volumes of incoming email.

In effect, they were relying on Mailinator’s proven ability to receive lots of email.

From the attacker's perspective, it doesn't matter much what is in the TO field. They just need to make sure that the emails get out the door. Mailinator is very good at receiving emails, the attack spread very quickly, and very soon the hhhhhhhhhhhhhhhh inbox at Mailinator was getting thousands of emails.

We noticed the activity early on, and shut down the inbound stream of emails to the hhhhhhhhhhhhhhhh inbox. Unfortunately, this did nothing to stop the attack. That's because nothing about the attack was happening via Mailinator. Mailinator was simply another recipient of the email. The attack could not propagate itself via Mailinator but it sure could send us email when other people propagated it. By the time we shut down the inbound stream, hundreds of thousands of emails to hhhhhhhhhhhhhhhh had shoved their way through our system. Any one inbox at Mailinator only shows 50 emails, and that inbox was (at peak) receiving a few thousand emails per second. Because the volume was so large, it wasn’t possible to read any of these emails at Mailinator. Before anyone could have clicked on one to read it, Mailinator had expired it to make room for thousands more that were pouring in.

The emails to hhhhhhhhhhhhhhhh were of no consequence to the attack. Even the name was irrelevant.

Strangely, we've seen a few articles mentioning that that inbox was the sender. Most even showed a screenshot on the same page contradicting that idea with the Mailinator address clearly in the TO field and one of the victim's contacts as the sender.

Just to be clear: the Gmail phishing attack sent email to a victim’s contacts using Google’s email servers and all emails were FROM another Google user. Each time the attack propagated, it also emailed TO Mailinator as a receiver, nothing more. None of those emails came from Mailinator, they came from Gmail.

It's true that all of the attack emails were TO:, but it seems pretty clear that if you're looking for where the emails came from, you'd want to look at the FROM: field.

Additionally, the emails can't be from Mailinator because Mailinator can't send email. It’s a receive-only service. The Mailinator system was not part of the attack - it was just a recipient like all the other victims. The only difference between us and the other recipients was that we received hundreds of thousands of these emails in a very short time.

If you visit that inbox now (here's a link to hhhhhhhhhhhhhhhh inbox - don't worry, it's safe to click, it will take you right to Mailinator), you’ll notice no such phishing emails. We turned the inbound stream of attack emails off very soon after the phishing scam started.

Service to our legitimate users was uninterrupted.

Mailinator remains, as always, the best place to get a free, disposable email. We can’t prevent people from sending email to us (receiving email is the whole point of the service!) and we still love our regular users: thousands of QA Teams that send us millions of test emails, and you - whenever you want to protect your real email address from spam.

Thursday, August 27, 2015

Mailinator's API : Closing the Loop for QA

Mailinator's API provides programmatic access to all email within the Mailinator system. If your QA department has a need for delivery testing, this is an unprecedented way to have immediate access to thousands of email inboxes.

Mailinator API docs

Since we launched the API a year ago, we've been constantly surprised about the uses people have found for the API. Testing signup systems (with a confirmation email) seems to be a popular choice, but other customers test marketing campaigns and test automated alert systems sending us thousands of emails each day.

The API works on both the public Mailinator system and the private domain system. For the public system you have instant access to any of Mailinator's millions of emails, obviously including the emails you send there.

If you're looking for more privacy, you can setup a private domain and only you (and your API token) can see emails that arrive for that domain.

If you're interested in accessing emails via API - Sign up at Mailinator today and try out the API!

Monday, September 22, 2014

Playing Wasteland 2? Find the Mailinator gun !

Mailinator has always been about vanquishing spam - and now in Wasteland 2, you can vanquish some Wasteland Wolves using "The Mailinator" gun !

Mailinator is proud to be a backer of the newly released Wasteland 2. If you're playing the game (and you should be!), be sure to lookout for the gun called "The Mailinator".

(hint: you might consider having one of your rangers specialize in Heavy Weapons !)

Saturday, November 9, 2013

Increasing Brand-Value of with a Web Comic

[This is a guest post by Marketing/Growth-Hacking consultant Martha Andrews - contact her directly at  Follow Martha on Twitter @another_martha]

We have been doing some investigation in increasing brand awareness for

Mailinator has always been a useful site providing free, disposable email - but analysis of the usage patterns of Mailinator indicated that users tended to use it on a monthly or bi-weekly basis rather than weekly or daily. In some ways this makes sense – the site provides a utility, but the use case for the general public isn't necessarily needed on a daily basis. When it is needed however - our goal is to make sure you think of!

In order to raise all usage levels of the site, we focused on public awareness of the site, expecting that an increased DAU (and MAU) would/should be an expected side effect.  I’ve frequented many trainings in the last year, and I cannot tell you how many times I’ve heard, “Create interesting and useful content and people will flock to your site…Its all about providing content.” 

But what content could we give to our users?  We already give away the service – we have a useful tool, and want more folks to know about it and use it.

Before creating content, something to consider is who is in our user base?  Web analytics told us the primary user base is male, ages 18-40 – think of the average Reddit user.  So how do we engage 18-40 year old men, and potentially other demographic groups?  How do we get them to think of more often?  What could we provide that would be of use of them?  Getting folks to think of the site more often, and giving them content and reasons to visit the site would likely expand their current usage pattern.

We tried targeted ads through traditional web and social channels. Specifically - we experimented with Google Adwords,, Facebook, and Twitter.  The ads provided momentary increases in traffic to varying degrees but nothing long lasting.  We can get more users to Mailinator any day of the week by spending some money, but that cannot be sustained given that doesn not generate direct user revenue.

During a recent site redesign we incorporated a new mascot of sorts – an amiable looking caped crusader we dubbed “Mailinator Guy” - the Anti-Spam Superhero. 
The more we lived with Mailinator Guy, the more often we started asking: what if we launched a web comic based on Mailinator Guy?  Would a comic be appropriate content?  If you've ever read Mailinator's FAQ you know the tone of the site is already quite tongue-in-cheek - we at least amuse ourselves.  Frankly the thought of bringing Mailinator Guy to life was simply too fun an experiment not to try.

ComicRocket has over 35,000 web comics indexed on their site alone, so competition for user attention is stiff.  However we found Facebook ads for the comic to be highly successful in engaging a new audience.  We think it works well because they are demographically targetable, colorful, eye catching and fun.  A thumbnail or portion of the strip is always displayed in the posts and ads.

We also engage our existing audience through the Mailinator Facebook page (with >30000 likes). There is an announcement on the page when a new comic is published. Additionally, the colorful thumbnail version of the strip is shown on the landing page and on mailbox pages at  We have found as we release a comic each week, we are slowly habituating our audience to check on a weekly basis – and if they are following us on twitter or are a Facebook fan, we have an excuse to contact them.

The feedback loop of the two sites is strong. provides the free disposable email utility that brings new users by itself. The site's design reinforces the Mailinator Guy character and encourages our primary demographic, arguably also the primary demographic for web comics, to follow the comic.  The site provides a weekly enticement for a visit. That visit keeps the Mailinator brand fresh in our user's mind causing the loop.

Of course some users of Mailinator will never care about the comic. And some users of the comic will never care about  And that's just fine - both sites have inherent stand-alone value.

At the time of this writing we have published six episodes of The Adventures of Mailinator Guy. Our advertising efforts, both paid and direct referrals from, have driven traffic that averaged 1,500 unique weekly users the first three weeks, to over 3,000 unique weekly visitors the following three weeks.  The most traffic occurs on Mondays when we have usually posted and announced a new episode.  Along with an increase in users, producing the comic has become more efficient and economical, and still pretty darn fun.

Importantly - traffic to has increased 15% in the 6 weeks since the launch of the comic and continues to grow.

These numbers are very encouraging but honestly the most important outcome is the increase in Mailinator brand recognition. The site's brand value will continue to grow and that's the real goal of this exercise.  

At the end of the day - everyone is happy.  More people know about the Mailinator brand - this makes us happy - and have either avoided some spam by using our free disposable email service, have had a laugh at the expense of Mailinator Guy - and his sidekick (you'll have to read the strip to find out about him), or both.

If you're up for following the adventures of Mailinator Guy yourself - here's the link to get you started:

The Adventures of Mailinator Guy! 

Wednesday, May 2, 2012

How to get your resume "Silicon Valley Ready" - Part I

Per my last post, I've been given the opportunity to review a nice pile of resumes. As I am prone to, this got me to obsess a tad over how the resumes were put together and more importantly, what each told me.

What I perceived as issues are, in retrospect, my fault, not the resume owner's. That's because, per the entire point of my last post, the start-up environment is radically different than the corporate IT department. And the latter is where many of these resumes came from (which is exactly what I wanted and asked for).

In many cases, I received a resume from someone that included the regular set of data - experience, education, skills, etc. But the ones that got me excited were the ones where the person included in the email links to the websites or mobile-apps they had built. As I've said - the number one selling point for you as an engineer to get a job in Silicon Valley is that you love this stuff. There's an age-old conundrum of new grads who say "Employers want me to have experience before they'll hire me - but how do I get experience if I can't get a job?"

In our business I'm happy to say - that problem does not exist. Simply because you don't need anyone to give you a job to build something. A website. A mobile app. Heck, a program that finds smaller sets of strings in larger ones.

I realized that's probably the number one thing I'm looking for. You can show me, with no doubts, that as a software engineer - you can build something. Start to finish.

Interestingly, I like to think that I also don't put that much weight into whether a project was a commercial success. If it was, that's nice but and maybe it's because you are not only a great engineer but you have an awesome product sense - who knows (it just might mean you were lucky too). And unless it wasn't a commercial success because it was poorly engineered, that's not really the point. The point is that you built it. Or at least some non-trivial part of it.

With that in mind - this article sprang forth on what I like to see in resumes. I'll point out that this isn't very different from what I looked for when I was on a hiring committee at Google (so there are at least some current Google engineers that are partially there because of these thoughts).

First - I propose a new section to resumes - at least for software engineers. In addition to Experience, Education, Skills, Interest, and References (not suggesting we remove any of those) - I propose we add Cool Stuff I Have Built.

If your resume is going to go over one page (which, personally, I don't mind) - I'm hoping it's because of this section.

Any project you did solo or had a major hand in - whether paid or not paid, million users or just your mom, I'd love to know about. Websites, iphone apps, android apps, desktop apps, open-source projects, github accounts - you name it. Solo or as part of a team (indicate that). But it has to be, in one way or another "finished". Even if your iphone app was rejected by the app store - you can point me to a link to see it. It doesn't have to be a product either - maybe its an open-source project. The bottom line is it is something that you "finished". You executed. Your idea became a living breathing application or piece of code that in some way some how you could show to people.

The section might be broken up into individual projects with bullet points about each. For example:

Project Name: Mailinator
Technologies used: Java, tomcat, (no database)
Team Size:5'11", 175lbs (haha)
Implementation details/challenges:Custom server architecture built as an experimental test-bed for highly-multithreaded server design. Custom SMTP server. No database as emails are stored in RAM with a custom compression scheme.
Notable Metrics: up to 25MM emails per day, ~20k users per day, runs on a single server (on purpose as part of a personal experiment to optimize the system).
relevant links:,

Surely you could add other bullet points too (and suggestions welcome, leave a comment to this post). But you get the idea.

My previous post resonated strongly with some people - that is, they were in "IT departments" feeling like they weren't growing technically. And as you can imagine, a resume telling me you did a payroll system is great - but it's not what (most) start-ups are building. But what if you haven't built anything? And your "Cool Stuff I've Built" section is empty?

Well .. fix that.

No one is stopping you from building something. No one said you're ready for a transition out of your current job today and as with much of life it's up to you to take yourself to the next level. But nearly any person that already writes software with a penchant for learning and some ambition can spend the next few months of nights and weekends learning and building. (And it's absolutely possible that your day job accomplishments belong in that cool stuff section too).

So if by day you're a payroll guy, but by night you're in iphone ninja - you've got my attention. Not only because you have the skills that I'm looking for - but that in your spare time, you're out doing great things. And instead of going out every night drinking with your friends - at least some of those nights, you chose to stay home and learn and build cool stuff. And why would you do something like that? Simple - you love this stuff.

(My start-up is located in Palo Alto and I am right now interviewing for the initial engineering team. We're well-funded, building cool stuff, and plan to change, ya know, the world. No matter where you are - if you're a software engineer, willing to relocate to San Francisco/Silicon Valley (and of course, love to build great things) send me your resume. or check out : Anatomy of a Spammy Campaign

Mailinator is a popular disposable email service. It's also become a great tool for QA Teams to test email receipt, acknowledgment, au...