Issue Problems with mail delivery to gmx.net,web.de

[Tamagotschi]

Big problems with mails to delivery GMX,WEB.DE
That is the feedback from GMX.
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Dear Sirs,

please note that, if your email header is not RFC 5321 and RFC 5322 compliant, your message will be rejected by our system.

This includes the following:

- Date and time must be correct
- The following email headers included in your message must be syntactically correct: Date, From, Sender, To
- The following headers included in your email must be limited to just one each: BCC, CC, Date, From, Sender, Subject, To

Therefore, we would advise you to check that the above mentioned information provided by your system is correct. Should you need additional support, please contact your System Administrator.
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Header:
[.....]
To: 12345 <[email protected]>
Authentication-Results: webhost1.xxxxxx.de;
spf=pass (sender IP is 176.199.xxx.xx) smtp.mailfrom=[email protected] smtp.helo=[192.168.xxx.xx]
Received-SPF: pass (webhost1.xxxxx.de: connection is authenticated)
To: 12345 <[email protected]>
From: xxxxxxxxxxx <[email protected]>
Subject: Testmail
Message-ID: <[email protected]>
[.....]
The recipient address is entered twice in the header.

Mails send from Windows Thunderbird and Outlook 365 via SMTP (webhost1.xxxxxxx.de).
Mails from webmailer "Roundcube" have a valid header! (the same server).

What's going wrong?

System:
Ubuntu 16.04.6 LTS
Plesk Obsidian
Version 18.0.28 Update #2, zuletzt aktualisiert: 7. Juli 2020 06:32:04

Tamagotschi

 

[Ankebut]

have you got found the problem?