Mail from Gmail Servers is Delayed Hours
I've been having a very peculiar problem for a few months now. Any mail sent to my server, via gmail (whether a gmail.com email address or a gmail-hosted private domain), gets delayed for hours before it gets to my inbox. All other servers are able to send essentially instanatly. But Gmail can take an hour, up to as long as 4 hours. Sometimes they do come in right away. If someone sends me 3 test emails, the sceond one might arrive right away, and the third might arrive 10 minutes later, and the first might arrive hours later. The delay seems to be totally random.
My server is 10.6.8, running Apple's Mail server. My DNS is all proper, my server's IP is a real, non-dymanic one with proper reverse set up. I have all my MX and SPF records configured correctly.
I do use the following four realtime databases on my server, but it doesn't seem like they could be at fault. All the mail does arrive eventually, and only gmail servers are getting delayed.
cbl.abuseat.org
sbl.spamhaus.org
xbl.spamhaus.org
bl.spamcop.net
This is one strange problem, that I'm not really sure how to diagnose.
Xserve, Mac OS X (10.6.8), 8 x 3.0 GHz, 8 GB RAM, Early 2008