If you’re using Apple Mail, and Gmail, and your emails seem to be getting stuck in your Outbox, grinding away for ages before popping up an infuriating “cannot send message using the server smtp.gmail.com”, try switching your outgoing SMTP server port setting to 587.
If you don’t know, here’s how to do that: Open Mail preferences (Command + , ), select Accounts, then Outgoing Mail Server list, and select Edit Server List. Select your Gmail account, hit the Advanced tab to the right of Account Information. You’ll probably have the option “Use default ports (25, 465, 587) selected. Switch to custom port, and type in 587. Close preferences, and your problem may be solved. Mine was.
If it goes haywire again, perhaps try ports 25 or 465. That will be my first fix attempt next time.
Google’s parabola seems to be flattening out. This is definitely a problem on their side.
If you found this useful, do please let me know.