This problem has been mentioned before apparently, but I haven’t seen anyone discuss a workaround.
With CAVS Incoming Email Scan enabled, I get errors from Thunderbird while checking mail.
“Sending of password did not succeed. Mail server mail.bellsouth.net responded: Invalid password”
Note that I successfully check several other accounts which are located on one of my mail servers, but the bellsouth ones (two of them) reliably fail this way while checking all accounts at once.
I can successfully check the bellsouth addresses one at a time in Thunderbird.
It would seem to be related to having multiple POP connections live at the same time.