Hi all. It seems that mutt fails to check the validity of a SMTP servers certificate during a TLS connection. In my mutt configuration I have set ssl_starttls = yes set ssl_force_tls = yes However, after performing the steps below I found that mutt did not properly validate the remote servers SMTP tls certificate. This means that an attacker could potentially MITM a mutt user connecting to their SMTP server even when the user has forced a TLS connection. Steps to test this: 1. I set in my hosts file the ip for smtp.gmail.com to be bound to mail.lolok.com in /etc/hosts 74.125.127.109 mail.LOLOK.com 2.Then I changed my set smtp_url = "smtp://MYUSERNAME () smtp gmail com:587/" to be set smtp_url = "smtp://MYUSERNAME () mail lolok com:587/" 3. I opened up mutt and emailed my self. I note that I saw mutt say "connecting to mail.lolok.com". I feel that this is an issue because mutt _does_ actually perform IMAP server certificate validation (at least it did when I last tested it :P).