Odd problem regarding address format

[AkutaSame]

I have noticed something odd as of late. One of my clients has reported being unable to receive emails from my domain. We are able to send to all other domains that we try, but this one just seems to absorb any emails that we send. They have checked all settings on their side. There is no sort of filtering going on.

Now comes the strange part. I'm looking at the active directory and Exchange. I notice something odd about the account through the Exchange interface (I have a distro group set up for sending email to my clients. One for each company as they have multiple contacts)... it's showing an additional domain/hostname on the email address (ex.: "myemail@domain1.com@mydomain.com"). Now, only these two (there are two accounts to the same client that are showing this same thing) are affected by this. Ok, I cannot seem to see any settings that would cause this, so I delete the accounts and recreate them. These accounts are STILL affected by this when the recreation is done. None of the information in their account point to this. I have tried copying other accounts that do not exhibit these behaviors, but these two accounts are still affected. This little bit of information was found (the two domains issue) after doing a track on the message and finding out that the emails were stated to be delivered to the local Store.

Any ideas?

 

[AkutaSame]

One thing that I forgot to mention... Upon being tracked, since it's being "delivered to local store" it is basically just putting it into their Exchange inbox... Well... I change the client SMTP addresses to be the respective address of the company the person works for. This is the first (of about 50+) set of user accounts that have done this.