Maybe this is why it’s “beta”.
Gmail’s POP documentation doesn’t mention anything about a message retrieval (download) limit.
In fact, there is one. It’s not new not new; I’ve found mention of it from 2007.
In my case I can download about 340 messages at a time. I think the limit is in place for a few minutes; I’ve been able to download about 3,000 over 9 or so sessions.
I discovered the problem while dealing with another geek tribulation (these things seem to come in multiples). I’d moved my ancient Eudora archive (abandoware) and, when testing it after the move, I saw my most recent messages were from August 2008.
So I tried again – but I was still in August. It took a few tries and cleaning up some other unrelated (but real) problems to sort things out.
Each time I fetch mail I get about 300-340 messages. It’s been that way for years, but I’d always assumed that was all there was. I didn’t spot the problem because I don’t read the email in Eudora, it’s just my local repository. Gmail is where I read and write.
Now I see that I’ve been slowly slipping behind the email wave front. Each time I downloaded I fetched about 300-350 messages, but there were always more in waiting. So the backlog grew.
This afternoon the backlog was seven months, but I’m down to two months now. I should be caught up shortly.
I haven’t noticed any particular limit with IMAP synchronization, so this may be a left over for a service they’re gradually deprecating.
Shame on Google for not documenting this limitation.