Comment 3 for bug 1672736

Also, if it helps, I often notice this problem with read messages in my inbox. That is, I've read the messages on my phone but not my elementary OS computer. I don't get a notification when the messages do arrive, which I think is normal behavior.

Full steps to reproduce:
1. Exit Mail.
2. Put the computer to sleep.
3. On another device, send yourself an email.
4. While still on that other device, open the email that you just sent.
5. Resume the computer from sleep.
6. Start Mail.

The message doesn't appear in the inbox for about 5 minutes. It's not clear that Mail is out of sync, and there's no notification when mail gets back into sync.