I was just about to make an issue about this, but it seems like other people have already brought this up.
We are also in a transitional limbo between having an on-premise Exchange server and Microsoft’s own servers, and we have the same email addresses set up in both. I’m looking for email clients where I make this work, since not even Windows 10 mail or Outlook can handle it at the moment.
Manually modifying the connection config yields this error:
It’d be absolutely perfect if Mailspring can handle this scenario, but I understand if there would be deeper implications to this that would make it harder to cater.
Possibly related: Adding a new account with same 'email'/from name results in 1 confused inbox