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Wednesday, April 29, 2009

Don't Let a Spam Trap Byte You!

As mentioned earlier, too many spam trap hits is one of the things that can affect your sender reputation. And, of course, sender reputation is the single most important item for getting your emails to the Inbox.

A study by Return Path found that IP addresses categorized as legitimate servers, but with even one spam trap hit, saw their delivered rate plunge to 38%. This is as compared to a legitimate server with no spam trap hits, which typically sees a delivered rate of 58%.

So, what is a spam trap or spamtrap, as it is also sometimes written?
It is exactly what it sounds like: It is an email account that was set up to trap spam ... it was created specifically to catch senders who harvest email addresses and/or attempt a dictionary attack, in which addresses are just made up, to see what doesn't bounce. A spam trap is an address that has never signed up to receive any email so, by definition, any email sent to such an address is spam.

How are spam traps created?
There are a couple of ways ... sometimes ISPs simply reactivate dead accounts. In other cases, they are new accounts, created solely for this purpose.

If you have these addresses in your lists, then either you are not properly pruning the lists or, if you purchased a list (NOT recommended), questionable practices were used to build it. Another way these email addresses can get on a list is when a subscriber makes a typo, when signing up.

What are the weaknesses of spam traps?
If a spammer discovers that a particular email address is being used as a spam trap, that party could send very large amounts of spam to that address. The spammer could also subscribe the address to any legitimate mail lists, that aren't double opt-in.

If a spammer uses a spam trap address as the sender addresses, any replies will be sent to the spam trap address. The replier is then also labeled a spammer.

If a spammer puts a spam trap address, along with many others in the TO or CC line, then if any of the receivers Reply to All on the message, the replying address will be considered spamming too.

Finally, a spam trap addresses is often shown in search pages like Google's, so anyone can write to it and this email will also be considered spam.

These actions give the spammer some control over the determination of what is considered "bulk unsolicited e-mail" by the anti-spam system.

How do you get rid of them, once they're on a list?
You want to remove spam trap addresses as soon as you can, but you don't want to inadvertently remove legitimate email addresses.

You must establish a policy for how many times you will send to a particular address, without at least getting an open response from it. Regularly remove addresses that reach this count.

The less often you send mail to a list, the more likely it is to harbor spam traps, as old addresses get converted into trap addresses.

Email addresses that are created by ISPs as spam traps need to be identified, if possible ... one approach is to send email to new (non-double opt-in) addresses, using a special IP address for a few days and then monitor the IP address for spam trap hits. There are a few sources of public spam trap data, such as the Spam Cop blacklist and Microsoft's SNDS service.

If no spam trap hits occur, the addresses can then be safely merged into your other mail lists.

So, how do you keep spam traps off your lists?
The best way is to only use confirmed or double opt-in. If you never send to an email address that doesn't confirm they want to receive your emails, then you will never send to a spam trap.

Whether you use confirmed opt-in or not, All Web Email can help you avoid spam traps.

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4 Comments :

  • Great post, Barb... very interesting stuff!

    I have a question regarding your last comment though, on how to keep spam traps off your list. You said:

    "The best way is to only use confirmed or double opt-in. If you never send to an email address that doesn't confirm they want to receive your emails, then you will never send to a spam trap."

    In the event a user confirms or double opts-in and years later let's their address expire for whatever reason... if the ISP now uses this old email account as a spam trap, would you still be in "violation"? Or, is this an instance of when the sender should be monitoring the number of unopened emails sent, and remove the address after a certain point?

    It sounds to me like this is a gray area because the sender would have had permission at one point to deliver their emails to that given address, but would later be "penalized" because the account happened to change hands.

    By Blogger Karl Ribas , At April 30, 2009 at 9:43 AM  

  • ISPs and other folks who've built reputation systems (like Return Path's Sender Score) are aware of those weaknesses, and take them into account. A single message to a single spam trap, just once, won't doom you. Reputation systems, for the most part look for patterns of recent bad behavior as a way to predict future bad behavior.

    For Karl's question: in every case I'm aware of (which includes all of the biggest ISPs), addresses aren't recycled into spamtraps until they've been inactive for some time -- often a year or more. So as long as you stop sending to addresses which don't accept the mail (always a 5xx SMTP reply), you won't have any problems with that sort of spamtrap.

    Stephanie Miller described some additional tactics in this article.

    By Blogger J.D. , At April 30, 2009 at 11:22 AM  

  • Karl, Thanx for your question and I apologize for the delay in responding. I was never notified of the comment, as I expected.

    J.D., Thanx for your response to Karl!

    It is correct that a single spam tram hit won't kill your sender reputation.

    On the other hand, by the time a deactivated email shows up as a spam trap, that address should have been pruned from the list.

    It is important to monitor open rates and keep your list free of address that just aren't interested, for whatever reason.

    By Blogger Barb Nolley , At May 14, 2009 at 12:30 PM  

  • PERFECT! Thank you both for clearing that up.

    By Blogger Karl Ribas , At May 15, 2009 at 12:14 PM  

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