Re: OT: dovecot with letsencrypt, K9 mail fails?

[Anthony DeRobertis <anthony@derobert.net>]

Dovecot (IMAP) is working fine here with K-9.

Since you're seeing different results in different clients, the most 
obvious reason would be a different behavior from the two different ways 
to connect to IMAP (or POP3) with TLS:

 * connect to port 993, start TLS negotiation
 * connect to port 143, run STARTTLS command, start TLS negotiation

(with POP3 it'd be 995 and 110).

You can debug both with OpenSSL's s_client:

openssl s_client -starttls imap -connect MAIL.YOURDOMAIN.COM:imap
openssl s_client                -connect MAIL.YOURDOMAIN.COM:imaps

(or of course change all the imap to pop3 to do POP3).

If you're seeing this on sending mail, that's SMTP — and there are 
/three/ SMTP ports you might be using: 25, 465, and 587. 25 and 587 need 
STARTTLS. s_client can deal with those, too.

Once you've figured out what's happening, then you can determine if it's 
something weird on your server or your VPS providers' network.