Recently I migrated from Yahoo.com to GMX.com. I used the feature "Mail Collector" to move yahoo mail to gmx. That seems to be working so far.
Meanwhile I noticed that when I am sending an email to yahoo from gmx, it gets bounced back, apparently from gmx. When I use the feature to make it look like it's coming from yahoo, it goes through.
I compared the headers of the sent emails and there does not seem to be much difference other than the from email address.
I don't seem to have much luck in getting either gmx or yahoo to help. This is happening with ALL yahoo addresses, not just my own.
Any help would be appreciated, how I can identify who is returning the email and how to get it resolved.

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