Using classic Outlook for Windows in business environments
I have been having the same problem over the past two years with an account that I have been using since 2011.
After researching, this problem has been reported happening spontaneously to people for 6+years now.
All of the sudden I was not able to receive important emails from different sources.
I would not know that I was not receiving them until someone would forward them to me.
I contacted Microsoft support.
Microsoft agents are less than helpful.
They go round and round trying to blame it on different possibilities.
Finally they admitted that they cannot fix the problem.
After going back and forth their final solution was to tell me that I have to have anyone who would be emailing me fill our a white list form for their servers.
This is not possible since I cannot know who is going to be emailing me and I cannot contact every server admin to fill out their whitelist form.
When I told them this they said that there was nothing else they could do.
I cannot conceive of why Microsoft cannot let the junk mail folder do its job and has to block emails completely?
Your best bet is to move to a different email service provider.
They do not want your business.