Identify mailbox provider with just email address (domain)

Question

I am looking at users signing up and granting authorisation to my app. My app will have read access to their calendar. But depending on their email address (at least the domain part), I want to know which provider I query. I.e. Microsoft, apple, Google, other. Its obvious if its Gmail.com but many will use a unique domain or may use a smtp provider such as trend to safeguard mail before it it's microsoft etc.

Answer 1

If you have user's credentials, you can try to retrieve autodiscover XML for the given SMTP address. Start at https://learn.microsoft.com/en-us/exchange/architecture/client-access/autodiscover?view=exchserver-2019 and play with Outlook connectivity analyzer at https://testconnectivity.microsoft.com/tests/Ola/input