I have my own domain (idrsolutions) but the actual email account is hosted by Microsoft. This can be accesed via a web client, IMAP or Exchange. Up until now, I was using IMAP to access it on MPro and Apple Mail.
Microsoft have now changed their IMAP setup so that you now require additional authorisation (using something called OAuth2). I have switched my Apple client to use Exchange protocol, but RISC OS does not support currently exchange or the new IMAP requirements.
However, there is a partial solution. It is slightly sluggish, but I am very pleased to say that I can use the web client in Iris to access my emails on RISC OS! In theory you should also be able to use Word, Excel and Powerpoint in the client. I could not get this to work but will retest in any new Iris updates.
So good and bad news on the RISC OS front if you need to access your email on a Microsoft server.