It may prove helpful if you post all settings done for the SMTP server.

Here are the SMTP config:

It is just as simple. Went through with support on it.

Since smtp config is working with Samsung mail it is not a problem with service provider.

Also note the K9 is no longer recognizing connection of the SMTP server.

It is in the app.

SMTP.service provider SSL/TL Port 467 No certificate

You might get more assistance if you gave the name of the smtp server.

Smtp.videotron.ca

A reminder, the problem only take place with Android version.

My PC app is working fine and yes it has the same SMTP config

Would be nice to have support from Mozilla team! In the mean while I am using Blue mail!

I have a similar problem using TB for android and Zen Internet as ISP. I set up TB for my ISP and it checks and says all the settings are fine. I then find I can send emails over WIFI from home, but not anywhere else. Using mobile data, I can't send emails from anywhere. I get a similar error "SmtpResponseParserException. Unexpected end of stream" I don't have this problem with Proton Mail, Outlook or GMail. I do with K9.

Hello, exactly! There was an update which broke the SMTP protocol and even with the lastcK9bupdate. This was not resolved. I am hoping that someone from the development team look at this issue!