You can talk directly to a mailserver using telnet on port 25. Replace mailserver with a real servername or use an IP address.

Connect to the mailserver.

telnet mailserver 25

Let's talk.

EHLO mailserver
MAIL FROM: fromemailaddress
RCPT TO: toemailaddress
DATA
Subject: This is a test please ignore
<Press Enter>
This is a test.
<Press Enter>
.
QUIT