Is there a simple way to time your mail server reposnse time? Specifically I am trying to figure out if a mail server is responding with in a 2-second window provided by verizon's sender verification setup.
In other words. If I send an email from myserver.com to email@example.com. Verizon.net will relay the message to a sender verification pool of mail servers. This pool will send a message to my server asking if the username exists. If it does not get a reposnse in two seconds it will not accept the message and return a 450 error.
Any thoughts would be greatly appreciated. The mail server is sendmail and it is running a greylisting program called relaydelay.