If you use dovecot or inside a bundle you may have problems using gmail as an imap client.
Due to Gmail’s recent enforcement of strict SSL security, you may have received something similar to the following error when attempting to access third-party email through Gmail:
“SSL error: Unable to verify the first certificate.”
Note: You may also receive a protocol error or an ‘SSL Certificate expired’ error.
So if your domain ‘mail.exemple.com’ pass the ssl test at qualys or digicert try to check :
> egrep -R “ssl_cert|ssl_key|ssl_protocols|ssl_cipher_list” /etc/dovecot | egrep -v “#” < Then, if you use letsencrypt check that all the config points to letsencrypt/live That's all Ubuntu 18,04 / Nginx / Iredadmin