not sending mails to certain recipients

[Otmarius]

My Exchange works fine, but I have problems with certain Domains.

i.e. I cant send mails to gmx.net. This mails will return with the error domain.name not found. The log file tells me that this message comes from gmx.

but there are also recipients. where the mail comes back with the error. Recipient not found. I should check the e-mail-address. This e-mail-adress exists. If i send an e-mail with Internet-Mail to this recipient. It does'nt come back.

Thanks a lot for your help.