Flask-Mail not working

I'm getting the following error while trying to send an email to confirm registered user's email-ID on registration. It would be great if someone could help. It was working fine on my PC, initially I was using threads to send email, but i read somewhere that web apps don't allow sending threaded emails, so I've removed that! Below is the screenshot of my error log: error log picture

[edited by admin: formatting]

you mentioned that you removed threading, but from the error log it seems like you are definitely using threads?