Freron MailMate

I have several private TLDs, and send email through pair.com using MailMate 1.13.2 (5673). All of this has generally worked flawlessly. I often use custom addresses in the "From" field as a way to tag messages. My account in MailMate is listed as "pobox@.com", but I often manually edit the From field to read "@.com". So "pobox@foobar.com" might be replaced with "myname@foobar.com" on a specific email.

Just today I am getting a lot of this error:
“5.7.0 From address is not one of your addresses”.

Even though the "from" is one of my private domains, MailMate seems to be sending my outbound traffic through the me.com server, which is bouncing it.

Sometimes mail goes through correctly, to specific addresses, which makes me think that MailMate is sometimes choosing the correct server for the account, but I can't see a pattern.

Also, and maybe related, I can no longer connect to my mac.com/me.com account. I have 2FA and had previously generated an app-specific password for the iCloud account, and I tried generating a new one, but no luck.

Any ideas? I do need to stay on Catalina for a while longer.

Best,

Steve