If you administer an email server as I do, it's very useful to have an automated monitoring system that checks often that it works properly.
My first try on any new feature I want to add to my non-fatally-critical systems is to use an external service, specially if it can be done for free. Whereas there is a number of server monitoring services, most don't include roundtrip email monitoring, at least on their free plan.
The only one I found to include it is...
It works like this: first you need to create and account and a first monitor. After that you can add more monitors. There's no visible limit to the number of them. At the time of writing the "login" link on that page is wrong, so in order to properly login later on, I had to bookmark https://mailflow.everycloudtech.com/
Data you are required to enter:
- contact email (not used for alerts), name, country & phone (used for alerts)
- domain to monitor
- number of email users (for their records I guess)
- path MX/direct (behave as a standard email client by querying the MX DNS record, or connect directly to the server)
- alternative email (alerts)
Step 1: Update your firewall settings
Step 2: Whitelist their sender servers if you're using spam filtering
Step 3: Create a test mailbox on your server and setup a forwarding rule to an ad-hoc account @everycloudtech.com
[optional] Step 4: Share on social networks
Step 5: Test the setup. Enter the email forwarding account created above & the system will test if it works.
Quite surprisingly for a "forever free" offer, when some monitor fails you will get a 20-seconds robotic phone call mentioning the domain that failed, plus an email alert to the "alternative email" you entered.
Once your monitors are active you can view an statistical performance graph of several periods, from the last 3 hours, up to the last 30 days.
I have compared & tried a fair number of free server monitoring services and the best overall I've found so far is StatusCake. It's one of the most feature rich and the only one I know that allows for unlimited monitors on their free plan. They also include an email monitor, but at the time of writing it's limited to verifying that the email server accepts an email they send, but it doesn't test further processing of it, e.g. forwarding it, as EveryCloud does.
Many other server monitoring services that include free plans don't include roundtrip email monitoring in their free plan. One of the least expensive is BinaryCanary. Their monitor looks better than EveryCloud's because it seems to verify your POP3/IMAP server also (I haven't tried it).
A good thing about EveryCloud is that they promise to keep their service always free, yet you may prefer to setup your own private monitoring. I've found there's an open source Python app for this, see Round-trip Email Monitoring on the Cheap (I haven't tried it either).
Note: I have no association with the services mentioned, other than being a greedy user of their free plans ;-)