In my experience Office 365 is even harder to deliver to. The email envelope can be in perfect shape and sent via sendgrid (their recommended partner) and it will still silently drop mails for no obvious reason and if it does deign to deliver them it will often mark them junk.

I’m only sending low volume transactional emails. The amount of time I have to spend tweaking the email content just to persuade Microsoft to deliver the mail is absurd.