kohlrak: I bounce emails off google, and yes it's a total challenge. After a few days or so, if you don't send another email, it'll automatically disable "insecure apps," which google defined as anything that is not google.
Yeah I've had to fight with that with Google as well, when my trusted Samsung email app stopped showing and sending email. Turned out Google had just decided it is "insecure", but luckily I was able to enable it again in gmail options because Google's own phone email app is crap, much harder to use.
As for MS, in one of my PC's Thunderbird email client I can't read certain live.com account's emails anymore because MS warned they think something "suspicious" is happening with that client so as a security measure it can do shit anymore, on that particular (Windows 10) machine. I logged into that account with a web browser but it wasn't fully apparent what the heck MS wanted me to do to make it trust that PC/client once again.
At the same time, Thunderbird can access that same live.com account just fine on a few other devices, which happen to be both Linux Mint and Raspberry Pi Linux devices. Funny that MS decided to cut communication to the client which is running on their own OS...
Whatever, who the heck knows what is their logic. Sometimes I feel both Google and MS do these kind of "security hardenings" in order to:
1. Try to get people to use their official clients for email.
2. Try to make it increasingly harder for non-MS and non-Google email servers from working, by constantly bouncing emails to Google/MS email users from any other servers for minor security "violations".
And they keep moving the goalposts constantly too just so that people not using their services and clients directly would have as hard time as possible.