TCP/IP and NFS FAQ
When your GUI mail client doesn't work, you need to know whether
the problem is at the server or the client. You could download
a different client (Thunderbird, if you are using Outlook or Apple
Mail) but why spend that time when you can test from the command line?
Note that some ISP's won't allow you to make port 25 connections
to anything but their mail servers. This is to keep viruses from
sending mail. If you need to test some other server, you may not be able to
without using a system that does not impose this restriction.
The lines preceded by numbers are typical responses. The
actual response may be different.
$ telnet mail.somewhere.com 25
Connected to smtp.somewhere.com.
Escape character is '^]'.
220 smtp.somewhere.net ESMTP Sendmail 8.9.3+Sun/8.9.1; Thu,
12 Oct 2000 04:39:40 -0700 (PDT)
mail from: email@example.com
250 firstname.lastname@example.org... Sender ok
rcpt to: email@example.com
550 firstname.lastname@example.org... Relaying denied
rcpt to: email@example.com
250 firstname.lastname@example.org... Recipient ok
354 Enter mail, end with . on a line by itself
look ma no headers!
250 HA00945 Message accepted for delivery
221 smtp.somewhere.com closing connection
You might also need to do a
first, and addresses may need to be in angle brackets:
Remember: some ISP'S block your outgoing packets, only allowing port
25 to their SMTP server. You won't be able to test any other server
if this is true.
If your server accepts secure smtp (it should), you can use openssl instead of telnet:
openssl s_client -connect mail.yourserver.com:465 -crlf
(If you don't use the "-crlf" you may have trouble using "." to end a DATA input)
I also have found Clean Code Email very helpful for command line testing.
If you have sendmail. you can use it from the command line with -v to see what really happens. See Debugging sendmail problems
See Microsoft's Connectivity Tester also.
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