This morning you mailed to 750,000 subscribers, a simple newsletter and you cannot understand why the delivery rate is beyond slow, in fact, it is crawling.  Your list members are all opted-in, you’re not black listed anywhere and this is a scheduled mailing, people are expecting it.  What’s going on?  You check with your list administrator who informs you your mail is being tarpitted. Huh? – With a little research and reading, you discover:

Tar Pitted or Tarpitting is closely related to the notion of the teergrube (German for tar pit):  a server that is intentionally configured to be sluggish as a common means of trapping address harvester programs. Can that really be the reason for your delayed mailing?

What and whys:

  1. Tarpitting is the practice of purposely slowing down email transmissions from reaching the mail server, typically by delaying incoming connections for as long as possible.  This practice is noted to have been developed as a defensive measure against a computer worm.
  2. Tarpitting can be created by adding specific delays between a set numbers of messages.  For example, the mail server can insert a 5-second delay between email messages after the first 50 messages are sent: which essentially can add days to your delivery rate (depending on how many list members you have).  Additionally the mail server can create a delay if the release time is extended with each invalid email address submitted.  If your valid email is caught up in a tarpit, your mail will eventually be delivered because the connection is never broken, just slowed down
  3. Tarpitting continues to be utilized because there is a belief that usual network abuses such bulk email spamming loses its effectiveness if delivery takes too long.
  4. Tarpitting employed by a mail server is done with the intention of discouraging bulk spammers, by offering low response rates because the slowed connections.  This in turn creates the inability to send volumes of messages quickly (and cheaply).
  5. The practice of tarpitting normally does not affect the integrity of legitimate email senders because the actual delay time is inconsequential for the typical recipient lists. (Mail server administrators can also make exceptions for legitimate mail.) ]

However, you’re not a spammer and you’ve been sending email newsletters for years!  If you find yourself with an unusual slow mail delivery, check with your ESP.  (Email Service Provider).  An ESP can usually research and discover if your mail delay is related to a tarpitting issue.  An ESP might tell you that bigger ISPs may tarpit mail on occasion for a variety of reasons, from internal issues to a perceived spammy subject line.  We’ve seen tarpitting occur without rhythm or reason other than the ISP decided that not enough people were clicking on the received mail, so therefore if might be spam.

If tarpitting becomes a concern, one option you may have is to get yourself whitelisted.  In some cases when your mailings are clearly whitelisted, tarpitting will not have an adverse effect on your email.  However not all ISP’s use or accept whitelisting which doesn’t help you if your dealing with such an ISP.

To be whitelisted is a good thing, as a whitelisted email may escape the tarpit slow down.  However, as mentioned this is not available to do with all ISPs.   Moreover, while being whitelisted is good, other classes may not be.  There is mail that can be greylisted or blacklisted.  Greylisting occurs when the sever rejects the connection causing the need for your email to be resent later.  Greylisting is based on the premise that spammers only want to connect to a mail server quickly, ideally on the first attempt with little hassle, while legitimate mailers will retry to connect to the mail server over longer periods.  If you’re sending from an unfamiliar IP address for example, you may be greylisted.

If you’re blacklisted simply put you are considered a Spammer.  Become blacklisted and you compromise your sender reputation and the IP address being used.  There are volumes of information written about Blacklists, a good topic for a future blog.

In conclusion, the necessity of tarpitting, and classifying email as greylisted, whitelisted or blacklisted is the direct result of the steady progression of spammers and other malicious coders of which there is no end in sight.  These proactive measures aren’t perfect, as you may well be aware of, but may be the best available for now.

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