Unexpected error - Thunderbird

Question

I replied to a message I received, and when I initially opened the reply window, there was an unexpected indent which I could not remove by pressing Backspace or by decreasing the indent. I ended up having to remove it by backspacing from the signature.

After I finished my response, I pressed send. The normal "sending" progress bar appeared, then this error appeared:

I pressed "OK", and it returned to the reply message. Every time I tried to send the message, the same thing occurred.

I noticed that the initial email (the one I had received) had the same indent. Every time I attempted to reply to the email, the same thing happened - the unexpected indent, and the error on send. I wrote a new email in response which worked fine.

What's going on?

Answer 1

You've configured Thunderbird to use an IMAP server when it needs to send email via SMTP. Open the "Account settings" window, scroll down to "Outgoing Server (SMTP)", and make sure all entries have the right server name and most importantly the right port entered.

Most outgoing mail servers use port 587 with STARTTLS; Some older ones use port 465 with old-style SSL/TLS. Yours probably has port 143 or 993 entered, which is completely wrong – these are the IMAP ports.

(That said, there's also the possibility that the server got misconfigured and someone accidentally told the Dovecot IMAP software to listen on SMTP ports...)