Most sysadmins share a slightly compulsive tendency to need proof that things are working properly. This is particularly evident if said sysadmin is setting up a corporate mail server – it has to work first time, no excuses.
One of the more painful parts of that process has been testing the newly configured SMTP server before delegating the domain’s MX to it. This involves speaking SMTP through your telnet client, or re-configuring your mail client to speak directly with the new server, then un-re-configuring it.
Neither is a difficult task, of course, but it’s a solid 30 seconds (minimum) that I’d rather not spend.
So I whipped up a handy little SMTP test tool, which does the SMTP-speak for you, and renders the whole conversation in your browser via an IFRAME.
Neat, handy, and of course free. Try it out.