You can easily test your mail configuration from a linux server with telnet.
$ telnet rhel1 25 Trying 18.104.22.168... Connected to rhel1. Escape character is '^]'. 220 rhel1.localdomain ESMTP Postfix HELO rhel1 # Note that "HELO" is not a misspelled. It is the command for telnet services. 250-rhel1.localdomain 250-PIPELINING 250-SIZE 10240000 250-VRFY 250-ETRN 250-ENHANCEDSTATUSCODES 250-8BITMIME 250 DSN MAIL FROM: ivan@rhel2 250 2.1.0 Ok RCPT TO: david@rhel1 250 2.1.5 Ok DATA 354 End data with <CR><LF>.<CR><LF> Subject: Subject goes here. Body goes here. . # End body with '.' and Enter 250 2.0.0 Ok: queued as 5C3E5E12EA # Quite interactive mail session with ctrl + ']' quit 221 2.0.0 Bye Connection closed by foreign host.
For a more detail description, please see http://www.ehow.com/how_5209651_use-sendmail-command-line.html.