Outgoing emails behaving oddly (SMTP error, remain in outbox, server reports multiple sent, only one really sent)

I have the weirdest problem with a new email account I just added to eM Client. Here’s the symptoms, which I’m sure they’re all related somehow but I can’t seem to find a solution:

  1. Whenever I try to send an email from this account (the other account I have on the program works fine), I get a connection error to the SMTP server (http://imgur.com/Qh189Dc).

  2. The message stays in the outbox and doesn’t disappear until I manually delete it from there (http://imgur.com/CKALiKL).

  3. The message goes out  from the first try** , **and arrives at the intended recipient. In my email provider’s (Zoho) web interface, it does appear as sent, but it doesn’t appear in eM Client’s Sent Items folder.

  4. Every time the folders sync, either manually or automatically, I get the SMTP connection error and the web interface shows another  copy of the message going out (http://imgur.com/pWDmPY6), even though the message only arrives  once to the recipient.

  5. If I close and restart eM Client, the whole bunch of supposedly sent messages finally appear in my Sent Items folder (http://imgur.com/MThHAgp). Again, the recipient only gets the message once, after the first attempt at sending it.

I’ve checked the configuration of the servers and everything seems to be working fine and configured according to the instructions provided by the email host (http://imgur.com/VoWTAYkhttp://imgur.com/5hLY7rihttp://imgur.com/4nA6z4I), so I’m definitely stumped as to why this might be happening.

Hopefully you guys can help me out, because I don’t really want to use the web interface for this account, but this issue is really annoying.

Thanks in advance!