Hotmail blocking mail
I've just fixed a long-standing problem, and it turns out the problem was "Hotmail".
I'm in a rural group of three churches, with a large team of folks doing all kinds of stuff. We use e-mail as the primary communications tool, as you would expect.
Two folks in the team kept not turning up to meetings, or complained they didn't have the agenda, and so on. So I did some digging: both use Hotmail as their e-mail.
I set up a hotmail.com address for me, and sent it some messages from my official and some other e-mail addresses. NONE arrived. Then I looked closer, and saw a little label on the mail screen saying "Junk". In there were all the messages I'd sent, marked "Microsoft SmartScreen marked this message as junk and we'll delete it after ten days."
They weren't particularly junky messages - unless you think a meeting agenda, a set of meeting minutes, and a message with the details of a funeral are "junk".
Those two folks now have webmail addresses on the Church system and are getting all their mail. But if you have Hotmail, check very carefully and very frequently what's in your "Junk" box. It may not be Junk.