The telnet client is no longer being installed by default on secure systems. So, how do you check that you can get to a remote port, like a mail relay? There’s been a trick in bash for a while, that I didn’t know about. Here’s how to get an idea:
2014-04-05 07:35:56 ec2-user@ip-172-31-9-61:~ 0$ cat < /dev/tcp/smtp.gmail.com/25 220 mx.google.com ESMTP st4sm62108693pab.34 - gsmtp ^C
This is great! I need to play more with it, but it works for a start.