As I’ve said before, I can usually tell when some ISP changes their filtering algorithm because I start getting tons and tons of calls about delivery problems at that ISP. This past month it’s been Gmail.
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.