Can't access Mailbox on MacBook Air (M2, 2022)

Further to my message last night, I tried re-entering my new Apple ID again this morning, and Lo! it worked.!! However, I was then asked to log into my other Mail accounts. So I used my New ID which didn't work, then I tried the old one which did. So I now find I have TWO Apple IDs which I don't think I should have. However, all mail boxes are now up and running on both Macs and as far as I can determine, on my iPhone and iPad as well.

Thanks for your swift reply.

No, I'm not using a VPN.

No, I haven't tried removing the Mail account. Might be worth a try. Is it safe and how do I do it?

I have an iCloud Mail account. It's always worked perfectly until now.

Only happened since using Migration Assistant. But it was annoying that my Mail files on my Mac were not being synced to the MacBook. I would have thought that was a basic requirement.

Afraid none of that works, because as soon as I click on the iCloud Mail account (which is shown as being "On"), a box pops up asking me to enter my Apple ID password relevant to the email address with which I have the problem. I have no idea what that ID is, or why it is different from the Apple ID which works with everything else. And it is only a problem on the MacBook.

Under Internet Accounts I get:

"Enter your password to continue using iCloud.

Verify the Apple ID password for marmot..................com

Enter password.

But it won't accept the password.

Hi Ingo2711

I don't know that that would be a good idea. I still can't understand what has gone wrong and feel it must be correctable without tangling up other stuff. My Apple ID password has been associated with both my primary and secondary Mail accounts and I've never had any problems until I used Migration Assistant to sync various files I had created on my Mac with my MacBook. Incidentally, I've never been able to understand why they were not automatically synced in the first place through the cloud. It appears that my Apple ID is now only associated with my original bigpond account but not with the icloud one I now use the most (and have for several years). I can't change the latter because it wants an Apple ID password which I don't know. I've always assumed it was the one I use whenever I've been asked for it and it always has worked. Until now. Usually when you have forgotten a password you can click on "Forgotten Password" and a system is provided for you to create a new one. This does not seem possible with Apple ID. I'm prepared to change my current Apple ID which is effective on bigpond to a new one, but I don't believe it will will be accepted by my icloud.com address, although it should automatically apply to everything, shouldn't it?

It's becoming a major problem because I travel with my MacBook whenever I go away, but can't send or receive mail on it. Any mail I do try and send from it just sits in the Outbox.

Well I think I've just done all that. I at last found found a way I could change my password for my icloud Mail, so I did. It all looked fine, I got a confirmation that my Apple ID password had been reset for my icloud mail account. This shows up in my Apple ID details. So I went to use it, and I now get a message that "An unknown error has occurred"

It's now midnight my time, so I'll grapple with it again in the morning.

No, well not that I am aware of. I had to change it once, some years ago, but I know what the original password was and have tried that but it doesn't work either.