Qmail: deferral: TLS connect failed; connected to

This guide will assist you how to solve mailing issue especially while using Qmail as your mail transfer agent. Usually customer will forward deferral bounce back email to us and showing which recipient that having issue sending with. This solution only applicable with Plesk Linux Qmail. There are some points you need to watch out and give attention to.

Check the MX of Recipient

First thing to do is check recipient email server MX server. Most case(s) I found Qmail having issue while sending to outlook server.

Fast Solution

The fast solution refer to Plesk is to change the MTA from Qmail to Postfix. This is fastest way with less burden. However, remember that there are customer(s) that need to use Qmail as-it-is rather than update to Postfix. ie. aux.com.sg.

Replace Certificate

I tried every single solution offered by Plesk, but some of them working, but sometime did not work. So the best solution we can do is to replace the certificate.

Install Let’s Encrypt

Make sure the Plesk already installed Let’s Encrypt. If hasn’t, then proceed to install first.

Generate Certificate

Now generate certificate from Domains > Let’s Encrypt > Secure webmail & www.

Configure the Default Certificate

Go to Tools & settings > SSL/TLS Certificate. Make sure for Certificate for securing mail cert changed to the one we just generated from Let’s Encrypt.

Try to Resend Email

Now try yourself to resend email and see in /var/log/maillog if there is still line :
deferral: TLS_connect_failed;connected_to_xxxxx