Mail going to spam - Cannot save postfix mail server settings

One customer complain that his mail don't deliver. Indeed i checked his mailbox and one of the returned mail was the following

This is the mail system at host host.localdomain.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<*********>: host[**.12.242.9] refused to talk
    to me: 550 mwinf5c11 ME Adresse IP source bloquee pour incident de spam.
    Client host blocked for spamming issues. OFR006_102 Ref***.***.41.243 [102]
Reporting-MTA: dns; host.localdomain
X-Postfix-Queue-ID: 3C0B2176F22
X-Postfix-Sender: rfc822; info@**********.com
Arrival-Date: Mon, 20 Apr 2020 21:31:14 +0300 (EEST)

Final-Recipient: rfc822; *******
Original-Recipient: rfc822********
Action: failed
Status: 4.0.0
Remote-MTA: dns;
Diagnostic-Code: smtp; 550 mwinf5c11 ME Adresse IP source bloquee pour incident
    de spam. Client host blocked for spamming issues. OFR006_102 Ref***.**.41.243 [102]
Return-Path: <info@********.com>
Received: from ********.com (host [IPv6:::1])
    by host.localdomain (Postfix) with ESMTPA id 3C0B2176F22
    for <********>; Mon, 20 Apr 2020 21:31:14 +0300 (EEST)
DKIM-Filter: OpenDKIM Filter v2.11.0 host.localdomain 3C0B2176F22
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=********.com;
    s=default; t=*******;
MIME-Version: 1.0
Date: Mon, 20 Apr 2020 21:31:14 +0300
From: ******** <info@********.com>
To: *******tard <*********>
Subject: Re: ***********
In-Reply-To: <********>
References: ************
User-Agent: Roundcube Webmail/1.4.3
Message-ID: <f187a6edbfc032a252bb678d9@*********.com>
X-Sender: info@*********.com
Content-Type: multipart/mixed;

After this i checked my score from and one of the problems was the use of host.localdomain

I tried to change the options attached to the photo to default (look attachment) but after clicking save and apply settings return to host.localdomain and localdomain

Can you help with this please?



Also another error from mail tester is the following

e check if there is a server (A Record) behind your hostname host.localdomain.
You may want to publish a DNS record (A type) for the hostname host.localdomain or use a different hostname in your mail software.

Howdy -- thanks for contacting us!

While we'll need to look into why that doesn't work for you, you can change all of those things on the command line as well, which is where I'd recommend starting.

Note that before changing any files, we'd recommend making a backup of them first.

What you can do is edit /etc/hosts, and first, ensure that you have an FQDN to use as a hostname (such as host.domain.tld) associated with the public-facing IP address on your server.

Next, ensure that there's a DNS 'A' record setup for that hostname.

Then, edit /etc/sysconfig/network, and look for a line beginning with "HOSTNAME=", and then ensure your new hostname is listed there as the hostname.

That'll be applied upon reboot, but you can also manually set the new hostname now by running the command "hostname host.domain.tld".

Lastly, edit /etc/postfic/, and change the mydestination line to include your new hostname. I'd also review the full file to see if there's any other references to the old hostname.

Once you're done editing, you can save that file and restart Postfix with "service postfix restart".

Thank you for your reply. Just to inform you i change in the attached photo instead of default which i could not save i deleted host.localdomain and put host.domain.tld instead and alo i deleted localdomain and wrote domain.tld

After this my score is 10/10 in mail-tester so if you also agree i won't make the changes of your previous message.