Date: 2013apr22 Protocol: SMTP Keywords: postfix, sendmail, qmail Q. How can I see what extensions an SMTP server supports? A. Connect and issue the EHLO command. The names of the extensions will be listed on multiple lines. This bash command line will do it:

echo EHLO <myhost> | nc <myserver> 25

Replace <myserver> with the name of your server. <myhost> should be your host name but anything will do. Notice its EHLO not HELO.