On certain occasions it is necessary to verify or to test different facilities for different mail servers razons but sometimes we do not have physical access to the servers.
A good way to test whether the postal services are functioning and to detect where the problem we can try to send email through the server using the telnet protocol.

To test the SMTP port 25, and know you can not send mail, or to identify where the problem better than a manual telnet session with the remote mail server.

Simple telnet session to the mail server
Uppercase / lowercase does not appear to be significant.

Type Server Response
Telnet server on port 25 220 (later identified - possibly with several lines of text + 220)
HELO our domain name 250 (followed by a message)
MAIL FROM: nombre_cuenta@dominio.com (eg, your mail account) 250 is syntactically correct
RCPT TO: destinatario@dominio.com (the recipient's mail account) 250 is correct
DATA Tells us that we can send the data, then CRLF CRLF end point
Then write the message CRLF CRLF point (eg, write a paragraph in a new line and then press ENTER) 250
QUIT Off Message

Popularity: 1% [?]