SMTP Watcher is designed to continuously monitor your SMTP servers and report to you if they go offline. The program is designed to sit in the window system tray and poll your servers periodically (every 5 minutes is a good setting). When a server goes down, a little balloon appears over the system tray alerting you of the problem.
Why is it necessary to monitor SMTP servers ?
Taken from my own experiences, I had a couple of incidents this year when the SMTP daemon on my server crashed unexpectedly. From an end-user perspective, nothing appears to be wrong. Outlook Express and related tools are still able to connect to your POP or IMAP server, but there is no mail.
Well, the situation when on for most of a day, and then I said to myself "gee it's strange there hasn't been any mail today!". Well, SSH over to the server and find that the SMTP daemon is down and no incoming mail is received.
The problem with this situation is that you're going to lose mail that people are sending you. Ideally, the sender will notice the SMTP server is down and retry the mail transfer at a later time, but you really don't know this for sure. If your server goes down, you could irretrievably lose some incoming mail.
What guarantees can SMTP Watcher provide ?
SMTP Watcher works by initiating a connection to your SMTP server and checking for a "hello signal" from the daemon. If the daemon is offline or has crashed, the connection will fail and SMTP Watcher can detect the error.
Similarly, if you entire server is unreachable (due to machine failure, unplugged cable, internet routing failure, etc), SMTP Watcher will not be able to make the connection and will report the error to you.
The only type of error that SMTP Watcher does not detect is if the SMTP daemon is online, and responding to connections, but failing due to some unknown reason. This would be a rarity, and is very unlikely to happen, but you should be aware of the possibility.
How many SMTP servers can SMTP Watcher manage ?
Gazillions of them! Seriously though, SMTP Watcher can probably manage as many of them as you'll ever type in. It's a multithreaded design, and each SMTP server is watched in a separate thread. You might run into trouble somewhere in the range of thousands of servers if you tried to watch that many, but I don't know of that many web administrators that need to watch thousands of servers!
Is it Freeware? Shareware? Commercial? or what?
SMTP Watcher is Shareware. The version that you can download is fully functional, and has no limitations, expirations, disabled features, or other junk. I allow you to evaluate it for an unlimited period, so it's very much like being a freeware application.