I know gmail was problematic for Apple Mail under Mavericks, and Apple kinda patched it up, and then Yosemite was supposed to patch it up even more and get things working properly. I had a lot of email problems under Mavericks, but Yosemite did seem to fix them. Until last week! Now, I'm having the same problems with my gmail account as I used to - Apple Mail will sit there, showing no new messages, and then when I check on my iPad or iPhone, suddenly I have dozens of unread emails going back hours! If I quit and relaunch Apple Mail, the emails show up. Likewise if I go Mailbox > Synchronise all accounts. I have one gmail account and one IMAP account for my private domain name, so while I could use the gmail website I still need to use a mail client for my private domain emails. I asked just now on Twitter, and got several replies from Yosemite users saying they had started experiencing the same "invisible" email problem which had previously been fixed. Any idea what is going on - or are there any Apple Mail (or gmail?) settings I need to check and change?