If they remove the "+microsoft" portion mailing me, that email is sent to my spambox and reported to spamcop, because I did not sign up with that address; the address I signed up with has the +etc infix.
Eventually I figure companies will get wise to this and I'll have to set up my own server which does the same trick with an underscore instead of the "+" sign.
You can make addresses on the fly like microsoft@cryptarch.fastmail.com (which will automatically be resolved and sent to cryptarch+microsoft@fastmail.com) and you'll save the hassle of having to run and maintain your own mail server.
You don't use a '+' at all in the fastmail email addresses you give out.
For example, say with gmail you have name+stuff@gmail.com, with fastmail you could use that if you wanted, but you can also use stuff@name.fastmail.com
If fastmail receives mail on that address, it converts it for you as if it had been sent to name+stuff@fastmail.com instead.
This happens entirely on the fly so you can make 'proper looking' emails without a '+'
I use mynamemicrosoft@mydomain.tld for each service, and i catch every email regardless of mail address.
Sure they can manually fool me or use more sophisticated regex to find their service name (and i can obfuscate it), but in practically all cases i know which service has leaked my address if i get spam against a certain address that's not the service i signed up for.
Related tutorial on how to set that up in Postfix: https://www.stevejenkins.com/blog/2011/03/how-to-use-address...
I recommend using a personal domain and a mail service that offers catch-all filters. Stuff regex on that and you can also filter all emails of this type into a specific folder.