My Wife has same issue. I deleted the app and reinstalled it, then I went back into Drafts and saw where it made an attempt to send out of Outbox and then went back into Drafts. This started back in May 2020 and has got progressively worse. Her account has a huge amount of emails that she never deletes and she is doing that over the next few days. I'll post back if that has any change but I think it is server-side.