I installed Dovecot on a local laptop running Buster. With no futzing at all, it works:
ghe@sbox:~$ telnet gb 143 Trying 216.17.134.202... Connected to gobook3.slsware.net. Escape character is '^]'. * OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ STARTTLS LOGINDISABLED] Dovecot (Debian) ready. I'm going to try reinstalling on the 'Pi. ... Seems to be OK now. Sorry for the noise... -- Glenn English