There have been two symptoms I’ve been hearing about. One is an increase in bulk folder delivery for mail that previously was reliably hitting the inbox. The other is a bit more interesting. I’ve heard of 3 different mailers, with good reputations and very clean lists, that are seeing 4xx delays on some of their mail. The only consistency I, and my colleagues at some ESPs, have identified is that the mail is “bursty.”

The senders affected by this do send out mail daily, but the daily mail is primarily order confirmations or receipts or other transactional mails. They send bi-weekly newsletters, though, exploding their volume from a few tens of thousands up to hundreds of thousands. This seems to trigger Gmail to defer mail. It does get delivered eventually. It’s frustrating to try and deal with because neither side is really doing anything wrong, but good senders are seeing delivery delays.

For the bulk foldering, Bronto has a good blog post talking about the changes and offering some solid suggestions for how to deal with them. I’m also hearing from some folks who are reliable that Gmail may be rolling back some of the bulk foldering changes based on feedback from their users.

So if you’re seeing changes at Gmail, it’s not just you.

This is something broken at AOL’s end, and the guys with the magic fingers that keep the system running are working to fix it. Right now there doesn’t seem to be an ETA on a fix, though.

Even if you are a sender who is able to stop the retries, you may see some congestion and delays when sending to AOL for the time being. Senders who don’t get the message, or who are unable to stop their MTAs from retrying 4xx mail will continue to attempt delivery of these messages until their servers time out. This may cause congestion for everyone and a noticeable  slowdown on the AOL MTAs.

AOL blog post on the issue

HT: Annalivia

The first step in talking about soft bounces is to define them. When I talk about soft bounces, I mean mail that has been rejected with a 4xx response during the SMTP transaction. As described by RFC5321, when a recipient MTA responds with a 4xx it is telling the sending MTA “Wait! I can’t take this mail right now. Come back a little later and try again.” The sending MTA will then continue to attempt to deliver the message until either it is delivered or until it hits the max delivery time, usually 3 – 5 days.

In a well behaved and RFC compliant MTA, messages that have reached the maximum time without delivery due to 4xx rejections will be converted to permanent rejections (5xx). With a correct MTA, this means too many emails in a row timing out shoud result in an email address being removed from future mailings.

For a number of reasons some ISPs, notably Yahoo, are using 4xx responses to slow down mail from some senders. Many senders treat this as a inconvenience and a frustration and try to figure out how to get around the rate limiting. The UK DMA published an article on soft bounces with the following words of wisdom.

Emails blocked in this way are recorded as soft bounces, so your soft bounces are important indicators of how ‘Spammy’ ISP’s think you are at a given point in time. They are an indication of a drop in reputation for the IP address you are using, uneven mailing patterns and/or an increase in the level of SPAM complaints your email is generating.  All of these things are things that you and your ESP can do something about!

This, in a nutshell, is why senders should not just grump about transient failures, but instead should look at their mailing practices. The ISPs using this technique to slow down senders typically are doing this on-the-fly, in that their limits are being put on mail that they see as problematic at that moment. In addition to the reasons given by the UK DMA, they are also monitoring complaints in real time and looking at the content of the message. If the ISP is seeing an increase in complaints about mail with a URL that is also in your mail, you may see rate limiting as a result. If the ISP is seeing an increase in complaints about mail from your IP, then you may see rate limiting as a result.

These are issues senders can address. You have the power and the technology to address the issue. Addressing the issue will improve your overall delivery.