Exchange was originally an X.400-based groupware system, SMTP support was somewhat of an afterthought. Exchange has a long history of not implementing SMTP properly with protocol violations and proprietary payloads (TNEF) and headers (e.g. Thread-Index)
I've been using "Microsoft 365" since 2012, outlook w/ a custom domain and all the grandfathered features. The +tag has always been supported, and I can't really tell what the difference between "Office 365" and "Microsoft 365" is, since the latter appears to include the former, if not identical.
Microsoft recently renamed a majority of their products yet again because if it wasn't confusing enough already, it's even more confusing now!
"Microsoft 365" now includes all of Windows 10, Office 365 (Office on PC) and Azure. This is more geared towards the home market.
Then, there's "Office 365 for Business" which as the name implies is more for business/corporate customers.
It looks like your custom domain is using the old Outlook.com/Hotmail architecture, which already supported +<tags> in email addresses - while Microsoft's corporate offering (running on a cloud based Exchange Server) still doesn't, and they're pushing support for it out later this year.
No it hasn’t. RFC 822 essentially says “local-part is whatever you want it to be” and defines no semantics. Certainly it doesn’t say “you can put a plus on and anything after that will go to the same mailbox”. That’s a far more modern notion, and one that is far from ubiquitous. Rather, it says things like this:
> The local-part of an addr-spec in a mailbox specification (i.e., the host's name for the mailbox) is understood to be whatever the receiving mail protocol server allows. For example, some systems do not understand mailbox references of the form "P. D. Q. Bach", but others do.
1982? Back then Microsoft's attitude toward the Internet was "embrace, extend, and suffocate." It made little sense for them to work with the nuances of standards, according their business model back then.
I have added this capability to every commercial web property I've worked on.
> I have added this capability to every commercial web property I've worked on.
I tried doing email validation the modern way: if '@' in emailfield then return True else 'email address needs an @'. The user gets a confirmation email anyway, and the sign-up process was literally name, email, tick a box that you read the privacy policy, and click continue, so they can just re-do that if they typo'd the address.
Iirc the boss decided to set requirements for a regex that I was to implement instead. Or maybe he made the regex and I tweaked it saying "this won't match .amsterdam domains", not sure anymore.
This has only been allowed since RFC 822 (1982). Is there any reason why Microsoft did not support this from the beginning (of Exchange)?