[Discuss] SSL problems with imapfilter after upgrade to Debian 11

[me at mattgillen.net (Matthew Gillen)]

On 8/27/2021 5:03 PM, Rich Pieri wrote:
> Server is behind firewall. It gets SSL certificates from letsencrypt.
> Dovecot is configured to use these certs. imapfilter had been working
> perfectly for a long time. Since upgrading to Debian 11 earlier this
> week I get these errors:
> 
> $ imapfilter
> Enter password for xxx at xxx.xxx:
> imapfilter: initiating SSL connection to xxx.xxx; error:1416F086:SSL routines:tls_process_server_certificate:certificate verify failed
> imapfilter: login request to xxx at xxx.xxx failed
> 
> My hopefully short term workaround is to disable SSL entirely with
> imapfilter behind my firewall but this is not a good solution.
> 
> Anyone have any ideas what Debian broke this time?
> 

Openssl s_client is your friend.

I'm not familiar with imapfilter, but the question is whether it does
STARTTLS.

If no, then
  openssl s_client -connect hostname:port

will tell you a fair bit about what the server is presenting to clients.
 (check the expiration on the cert; LetsEncrypt is only valid for 90
days; maybe your auto-renew is broken?)

If it does STARTTLS (start with a normal TCP connection, then transition
to TLS), then you need to specify the protocol; looks like IMAP in this
case:
  openssl s_client -connect hostname:port -starttls imap

Hope that helps,
Matt