ISPs Respond to High Volume and Reputation Plays a Role

It’s depressing but true: there is more spam being sent than ever before.

In fact, ReturnPath's ISP and other receiver contacts report a tripling in the amount of spam coming across their networks in the past six months. This volume, combined with the increased volume of permission-based email typically seen in the fourth quarter means that overtaxed networks may process email slower as the volume backs up the systems.

As a result, your campaigns may generate higher-than-usual number of soft bounces including 421 and 451 SMTP error codes, as well as connection time outs. In particular, these system time outs could become more common as we move further into the high-volume holiday season (which kicked off with Halloween and will intensify after Thanksgiving).

What’s more, ISPs are prioritizing email traffic based on complaints, bounces, and other data to allow senders with better reputations to have their email delivered first. Once again, it’s all about reputation.

Minimize the chance that you will experience increased soft bouncing by achieving and keeping a good sender reputation. Be extra vigilant in keeping your unknown users rate low, maintaining low complaint rates, processing feedback loop data, honoring your communicated sending frequency and making sure your unsubscribe process is easy and works.

Also make sure your infrastructure is in full compliance. All your IP addresses should have valid reverse DNS information. Your systems should not be open to abuse from open relays and open proxies. Also double check that your sending domains are being authenticated using SPF and DomainKeys.

How do you know if volume thresholds are causing problems for you? You may see a sudden drop in deliverability at an ISP where you previously had been delivered. If this happens in combination with unusual bounce reporting from that same ISP, then that is a good indication that volume thresholds might be the problem.

If you see this pattern, consider metering your email sending volume and sending at off-peak times during the day (early morning or later in the evening) to lessen the competition your messages face as they pass through the receiver gateways.

We also recommend testing the time intervals in which your system resends the messages that were bounced back. Part of how your incoming email is evaluated by ISPs and other receivers is whether or not a retry is attempted. Traditionally, email senders had been advised to retry sending within 15 minutes of the first attempt. We are now advising our client to schedule retries between 30 and 60 minutes, since shorter time intervals can place an undue burden on already overloaded systems. One other possible solution is to utilize mail server functionality that allows for you to hold back the sending on certain ISPs while allowing the rest of your campaign to move forward. If you’re a large volume mailer, this could result in large retry queues. Make sure your hardware and applications are equipped to handle this.

As they constantly do, receivers will adjust their thresholds to accommodate the additional spam, but the seasonal traffic spikes permission marketers does compound the problem. Knowledge is power! Watch your bounce codes and act swiftly and appropriately to protect your email revenue this season.

Source: ReturnPath