My first concern is seeing server name begins with 'pop', yet error message indicates imap. Maybe if you post server settings, some ideas will surface. Also, it may help to review that each account is using a separate SMTP server, as that is a common issue when users have more than one account on the domain.

smtp.xplornet.ca

Port 465

SSL/TLS

Normal Password

thehawkesr@xplornet.ca

Pop Mail Server

Port 110

STARTTLS

The problem started right after Thunderbird Up date 2/7/2024 115.7.0

Hope this helps

This may not work, but I've seen many email provider changes in past year. Try this: smtp.xplore.net with port 465 and SSL/TLS if that doesn't work, try smtp.xplore.net with port 587 and STARTTLS

Port 465 Message says timed out Port 587 Message Sending of the message failed. SSL received a record with an incorrect Message Authentication Code. The configuration related to smtp.xplornet.ca must be corrected.

You have another email address, also with xplornet.ca? Compare for any possible differences. I am not familiar with that email provider.

Same problem. I've made sure the smtp infor was the same except for the email address. Both are charter.net: Description is blank Server name is mobile.charter.net port 587 / default 465 SSL/TLS Normal email address when I try to send via this address I get please check the address. I've used this client for many many years without incident. suddenly I can't send through this address

I suggest putting a unique name in description field, such as the email address and then recheck the account setting pane that links to SMTP server to verify that is the SMTP server in use.