As I use this frequently to test remote mail hosts for one of my clients, I figure it deserves a spot here. This will allow you to manually test a remote mail server using telnet and port 25:
First get the mail server address for a website. We will use gmail.com for our example:
dig gmail.com mx ... gmail.com. 1654 IN MX 50 gsmtp183.google.com. gmail.com. 1654 IN MX 5 gmail-smtp-in.l.google.com. gmail.com. 1654 IN MX 10 alt1.gmail-smtp-in.l.google.com. gmail.com. 1654 IN MX 10 alt2.gmail-smtp-in.l.google.com. gmail.com. 1654 IN MX 50 gsmtp147.google.com. ...
Not sure if there is a specific mail server to choose, but I usually choose one with a higher priority. In this case I will choose gmail-smtp-in.l.google.com to test from my server:
telnet alt2.gmail-smtp-in.l.google.com 25 Trying 184.108.40.206... Connected to alt2.gmail-smtp-in.l.google.com (220.127.116.11). Escape character is '^]'. 220 mx.google.com ESMTP y37si31029380iky.4 HELO outofcontrol.ca 250 mx.google.com at your service MAIL FROM:<email@example.com> 250 2.1.0 OK y37si31029380iky.4 RCPT TO:<firstname.lastname@example.org> 250 2.1.5 OK y37si31029380iky.4 DATA 354 Go ahead y37si31029380iky.4 This is a test. . 250 2.0.0 OK 1230083982 y37si31029380iky.4 QUIT 221 2.0.0 closing connection y37si31029380iky.4 Connection closed by foreign host.
A few notes:
On most email servers you do NOT need to include the < or > tags around the email address. Stricter mail servers require it. On gmail if you do not include them you get a nasty '555 5.5.2 Syntax error'.
Don't do anything nasty or stupid, as you can be easily traced through the remote servers mail log. This how-to is to help remind me and to help you trouble shot potential email issues with remote servers, or even to your own server.