A couple weeks ago, I updated my iMac from MacOS 10.10 Yosemite to MacOS 10.12 Sierra. In doing so, I encountered a confusing and vexing glitch. I have a personal Gmail account, set to IMAP. I have the Gmail account setup as an internet account on my iMac. I also have my Gmail set up to work on my smartphone. Up until I updated the iMac to Sierra, this arrangement worked fine. Since updating, I cannot send any Gmail from my iMac using my personal Gmail address. Other Gmail address I use in Apple Mail work fine, and I can receive my personal Gmail without difficulty. But sending from my personal account is impossible. I check the settings. The System Prefs show my Google account is set up OK, although it doesn't let you actually look at the settings. In Mail, my personal Gmail is listed as "offline", and strangely, the outgoing server is listed as POP, not IMAP. I have no idea why and less of an idea of how to tinker with the Mail account settings. If I access my Google account in the Google Chrome browser, my personal Gmail address sends and receive e-mail smoothly as always. What can I do about this?