SMTP server terminates connection before sending QUIT command

Question

We have written a simple (standard .net tcp async logic) SMTP listener which listens on 25 port for incoming connections from other SMTP servers.

It process all mandatory commands like FROM, RCPT TO, etc.

With some servers it works well but, some SMTP servers (like Microsoft outlook) terminates connection before sending QUIT command and then re-send the same mails again and again.

Anything we have missed?

Answer 1

Here is the answer:

354 Start mail input; end with<CR><LF>.<CR><LF>

we had to send <CR><LF>.<CR><LF>