If you’re looking to verify if an email address is functioning properly there are a couple of methods available.
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You can actually connect to mail servers using the telnet command. Here’s an article that sums up the process rather easily.
If you’re not familiar with using a terminal, which is now available on Windows then you can read this article that I’ve developed.
There are a number of online services that allow you to check if any email address is functioning.
If you know of others that work well, please comment and I will add them.