Still getting : "Hop count exceeded - possible mail loop" after five days.

Hello,

I have set up an office365 P1 account for a client of mine.
I did not have any issues with 2 other domains in the same subscription. But with one domain I still get the error "Hop count exceeded - possible mail loop" even after five days.
I already connected to powershell with these commands, but still receive the same loop error :

set AcceptedDomain Identity <DOMAIN> -OutboundOnly $true

set-AcceptedDomain identity <DOMAIN> -OutboundOnly $false     

Does any one have a solution for this problem?

I'm getting quite desperate.