UCS mailing list & mail relay

Hi Forum,

I have a question regarding email relay and mailing lists.

I was quite frustrated about my email server being ignored/blocked/categorized as spam. Despite correct SPF, DKIM, DMARC configuration and a score of 10/10 at mail-tester.com and high deliverability at all major email providers I have constant problems delivering to outlook.com and hotmail.com addresses. I know this is a widely discussed problem…

However, I now use a mail relay at mailjet.de. Everything is fine and thanks to this forum configuration was easy.

One problem remains: I use a UCS mail list for a defined number of users who have email addresses with domains not owned by me. Example:

UCS Maillist: friends@mydomain.de

UCS User : Email address

Me : me@mydomain.de

UserA : Alfons@gmx.de

UserB : Bertold@gmail.com

UserC : Claudia@hotmail.com

Sending into the mail list friends@mydomain.de is restriceted to only members of the list. I have registered access to the mailjet mailrelay for *.mydomain.de, so me@mydomain.de and friends@mydomain.de are allowed to use the mail relay.

When I send an email from me@mydomain.de to friends@mydomain.de the email is rejected because @gmx.de, @gmail.com and @hotmail.com are not allowed to use the relay.

In my understanding this is strange because sending would be:

me@mydomain.de : to : friends@mydomain.de : to : mailjet relay : to : Alfons, Bertold, Claudia

What am I missing here? Can anyone help?

Thank you!