Connection error (Failed to reach the server)!

Good afternoon. I installed mail in a box to my server with ubuntu 18. But when you try to send a letter to any address through the roundcube client, when you click on the send button, the following message appears:

Here is a link to a screenshot if the text is hard to read: Frame 1.png - Google Drive

I registered all dns records and installed all certificates.
I painted over the data, because the domain and server are not mine, but belong to the organization.

I can receive emails and they are visible in the roundcube client. And if I connect the imap server to a third-party client (for example gmail), then I can send letters and they even reach, but end up in spam.

I reinstalled the system several times and re-registered all domain records, but I could not solve this problem.

How can I make it so that I can send emails without problems through roundcube and how can I make sure that my emails do not fall into spam on other mailboxes?

I will be very grateful if you help me and maybe I will thank you somehow.

What version of MIAB did you install? As of a few days ago, the current MIAB version is 60 and it requires Ubuntu Server 22.04, not 18.

Re your mail not going into spam. If you’re setup correctly (with DNSSEC) you won’t have much trouble with properly complying email services, but some of the big ones deliberately don’t comply with the standards. See older forum posts re getting Microsft and Google to accept your mail - for MS it’s easy enough, less so for gmail but I found sending from gmail to my domain seemed to help.

I installed version v57a. DNSSEC was not installed, as you can see from the screenshot. After all, it says that this entry is optional. DNSSEC is it mandatory to install?

Re DNSSEC - not mandatory but improves your emails spam rating, so recommended if you want to send email to others! See other threads in the forum re the spam problem.

Re the connection error - looks like a roundcube problem, with which I can’t help much, but roundcube seems reasonably reliable, so it’s likely an issue with your setup. I would check that ALL the required ports are open between your server and the internet, and look have a look at the roundcube forums.

All ports are definitely open. I wrote rules for UFW and checked each port individually through the telnet command.

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