If anybody else gets emails stuck in outbox/drafts, found a solution in certain scenarios

I tried several times to send an email that would not leave my outbox, with no helpful error messages getting provided. I was using a reliable IMAP email application  - Thunderbird for both Android & Windows Desktop. By saving the email in my Drafts and then trying to send it out via the web app, I think I found the cause: There was a javascript popup that interrupted the sending but did not produce any errors, which alerted me to the fact that the sender of the email to which I was attempting to reply had used the phrase "I have attached" and the web frontend (which I had not been using) evidently was expecting me to attach something in my response.

Bad scripting.

I hope this helps someone.