This is at least my third mention of a problem between Gmail IMAP and Mac Mail, but I'm raising it again because many others have the same issue and I believe resolution is near. Switching from my hosted Exchange server to Gmail's IMAP service has worked well in general, but for no apparent reason it just tanked for me about three weeks ago. There were no changes in my environment, nor to Mac Mail and I suspected something changed on the server side.
I spent the next several days doing my own testing and isolated the issue occurrence only when Mac Mail was running. No other client caused the delivery delays and constant message caching I was witnessing. My next step was to share my information directly with the Gmail support folks and over the past three weeks, I've written well over 1,000 words to them presenting the evidence in detail. It probably shouldn't have taken that much effort, but I really don't mind because I believe I finally got their attention on the right information. Here's what they said:
"We are aware of this problem, and our engineers are working diligently to implement a solution for all users. We apologize for any inconvenience this issue may have caused.
In the meantime, during the course of our investigation, we've identified specific technical circumstances that would allow us to implement a fix for your particular account by placing it under maintenance for up to an hour. You'll be unable to access your account during this time. Please respond to this message if you'd like us to implement the fix, and also please provide general timeframes and dates during which the maintenance of your account would be least inconvenient."
I provided them with the OK to take my account down and then proceeded to have no e-mail access for appproximately 18 hours... not the 1 hour I was told. I actually didn't mind because that tells me all the more that there's an issue between Gmail IMAP and Mac Mail. Unfortunately, I saw no change in the mail behavior after the maintenance, which was reinforced by the next message from the Gmail support team:
"We regret that your account will require additional maintenace in order to resolve this issue.
Please note that your account will be placed under maintenance again starting at 5:00 pm Pacific Time. We'll make every effort to complete the maintenance as soon as possible, but please note you won't be able to access your account for several hours while it is under maintenance."
I set up a time for that maintenance (yesterday), but didn't see the account go down. It was just under maintenance a short while ago for a brief time, so I'm hoping that the issue is now resolved. If so, I anticipate a note from the support team indicating it is. If I'm correct in my premise that there's an issue that's more global than just my account, I expect it will get quietly fixed on the back end although I'd hope for some public information to come from Google. Needless to say, I'll be happy when it is resolved. I can avoid the problem by keeping Mac Mail closed and using the web or other clients, but I like to have choices about what clients I want to use.