Joey wrote, at 10/20/2008 12:42 PM: > I just wanted to confirm something. > > We are defining 3 servers for MX and the first one is basically nolisting. > > Should any server trying to deliver to the first mx IMMEDIATELY try to > connect to the second, or should we see a delay like with greylisting? > > My understanding is there should be no delay, but we are seeing some > messages coming in 30 minutes later delivery wise versus when it was > sent from the client.
This depends on the origin domain, and involves a variety of factors, including the software they use, their policy, load balancing, etc. In my tests, most hosts retry immediately, and there is no noticeable delay. Some sites, however, appear to put failed connections back into a pool, and retries may occur up to an hour later (not always from the same host). You can monitor this with tcpdump, and verify the second connection against your mail logs. This is the only way to prove that there was no delay introduced at the sending site. A lot can happen between the sender's client and the recipient's mailbox.
