assuming we have a good chain of trust between us, all communications are secure.
That is not correct - an SMTP server will deliver email to another SMTP server in the clear [1]. Your ISP or the ISP that the remote SMTP server is using can read it. Even then - running an email server from home has certain issues such as port 25 inbound blocked, or most email servers will drop email from residential IPs.
The only way to make sure communication is secure is to use an email certificate with encryption or GPG. These would have 2 benefits: the email would verify who it came from (email can be easily forged) and the contents would be encrypted.
Comments
That is not correct - an SMTP server will deliver email to another SMTP server in the clear [1]. Your ISP or the ISP that the remote SMTP server is using can read it. Even then - running an email server from home has certain issues such as port 25 inbound blocked, or most email servers will drop email from residential IPs.
The only way to make sure communication is secure is to use an email certificate with encryption or GPG. These would have 2 benefits: the email would verify who it came from (email can be easily forged) and the contents would be encrypted.
[1] http://security.stackexchange.com/questions/12087/if-i-send-...
Well, I'm actually a big advocate of PGP and encryption.
however, I know that SMTPd's (notably: postfix) will negotiate TLS where available, and you can configure it to fail if speaking plaintext.