Earlier I wanted to look at something in my Mail prefs but, as soon as I opened them, the status of may mail account changed to "Offline". When I tried to get it back online I got a message that neither my User Name nor my Password were recognized.

I re-entered both but kept getting the same message. During all of this I sent myself some test messages but did not receive them on my iMac. I checked the ISP's webmail account and the test messages had arrived there.

Then I checked my iPad but it had a message similar to the iMac message ....about not being able to connect to the server. I assumed that two machines not receiving must mean the problem was with the ISP server, not my Mail app(s).

Then, like magic, the test messages came in, so I sent a new one which went and was received successfully. However, even though mail is coming and going, the Prefs panel on my iMac still says "Offline". Why would that be? Is it an issue with the app or can it be some weird thing with the server?



NOTE: There is an extenuating circumstance. Historically my ISP, Telus, has had big issues with server failures and have recently decided to move their clients to something called "enterprise-grade G Suite" and are doing it in a phased method. I have not yet been moved but wonder if all their phasing activity could be screwing up other things.

Have you quit and relaunched Mail? Have you performed a cold boot (ie. powered down, paused a few seconds, then restarted)?

Yes to both. I also took these actions:

1. Booted into Recovery and ran Disk Repair from Disk Utility
2. In Cocktail, ran the Daily, Weekly, Monthly scripts
3. In Cocktail, rebuilt Launch Services database

Is it not reasonable to assume the issue might be with the ISP's server, not my Mac software, since the issue was common to both my iMac and my iPad?

I had a similar problem with Mail, but it was not my ISP (Spectrum): I could receive emails by using Outlook instead of Mail (Outlook is not my first choice). In addition, I could log into Spectrum's webmail with the same password. The solution was to create a new account in Mail. This was Apple's idea and it has worked.

Several years ago, when I was using MS Entourage, my account became corrupted and I had to do the same thing.

By "create a new account in Mail" do you mean an account with a new e-mail address and password, or just delete the old IMAP account and recreate it as new? The latter is safe to do, the former requiring some (more complex?) transitioning.

I made a HUGE MISTAKE in deleting the old account. The Apple tech told me to do it and I did, without thinking. The result was that I lost all the emails associated with that account and had to do a lot of legwork to retrieve them. You can see the whole sordid mess in this thread. Had I kept the old account, all the emails would have been there, even if I had trouble with the account.