According to the RFC for SMTP (RFC 821), all commands must end with carriage return + linefeed, so it sounds like all of your commands should end in \r\n. The SMTP server should issue status messages along the way, so it may be a plus to check that everything is going as expected.

Update: I just tried your code cut n' paste with my own server after adding the \r\n to all lines, and it worked like a charm.

Guildenstern
Negaterd character class uber alles!