I very often have to fight with developers who claim that they are unable to send notifications from their apps. Even after sending them confirmation of a successful telnet, they still argue. This is how I silence the doubt:
Telnet to the server via port 25.
1. Key in “EHLO example.com” and hit enter.
2. Key in “MAIL FROM: email@example.com” and hit enter.
3. Key in “RCPT TO: firstname.lastname@example.org” and hit enter.
4. Key in “DATA” and hit enter.
5. Key in your message body and hit enter.
6. Key in ” . ” and press enter.
If you received the mail then your SMTP is working fine.