What is SMTP tarpitting? What are SMTP tarpits (or tar pits)?

You create innovative content your subscribers love, and want to make sure they receive the emails you send. Fortunately, SMTP tarpitting is designed to thwart spammerswhile causing only a slight inconvenience to legitimate senders like you. Nonetheless, tarpitting can still cause delays and confusion if you don’t understand how it works or why it’s in place. Keep reading to learn more.

 

SMTP tarpitting explained

What is an SMTP tarpit? Simply put, SMTP tarpitting is the process of slowing down bulk email delivery in order to block spam. Here’s how it works: you send an email to your list of loyal followers. During the Simple Mail Transfer Protocol (SMTP) session, the mail server notices the emails were sent out in bulk, and gets suspicious. To protect against spam, the mail server decides to wait awhile before delivering the email to the recipient's inbox. This delay is called a tarpit, and its duration is referred to as tarpit time.

Tarpit time varies from one mail exchange (MX) server to another. Some older MX servers respond slowly simply because they’re not adapted to more modern email usage. In most cases, however, the MX server replies within less than five seconds. Even so, five seconds of SMTP tarpitting per address could pose a significant roadblock to spammers, whose intention is to send as many emails in as little time as possible. For example, if the spammer sends the same email to 20,000 recipients, at five seconds per recipient the whole process could take 100,000 seconds, or close to 30 hours! Spamming systems are built for speed and some will even give up on sending bulk emails if they encounter significant delays.

This can still frustrate non¬-spammers sending out legitimate emails. As the sender, you want to maintain a clean list and ensure prompt email delivery. But SMTP tarpitting works on both valid and invalid email addresses, so after all that waiting, you might eventually receive a Non Delivery Report (NDR), also known as a bounce email.

 

How does SMTP tarpitting affect me?

You produce high quality content, so you want to make sure it gets delivered to the right audience. Verify the email addresses on your list to keep on top of your sender score. You can do this with a validation service, but choose it wisely.

Your email validator initiates a session with the recipient MX server, so if the recipient server imposes an SMTP tarpit, your validator won’t generate a sure answer right off the bat. With some validators you’d need to retry manually, but at Verifalia we have a simpler, more convenient solution.

Verifalia’s unmatched validation service offers anti-tarpit tools with customizable features so you can select the right plan for your own needs. We provide three quality levels to choose from: our standard quality profile allots you five seconds of anti-tarpit time. Our high quality profile exceeds industry standards, giving you up to 50 seconds of anti-tarpit time, while extreme quality lets you choose anywhere from one second to five minutes.

What does this mean for you? It means Verifalia will validate the email addresses in your list, even in the case of an SMTP tarpit. Count on Verifalia to clean your list so you spend less time waiting and more time delivering excellent content for your email marketing campaign.

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