Reply goes not to the sender

Hi,

I have strange routing problem.

The user A sent a mail to user B, and I get the reply mail of B, not the original sender.

I checked a lot of things and I found a curiosity.

The alternative name is correct in the original sender’s person document.

But in his client, at the Tools/Preferences, Mail/Basic tab I’m the alternative name of his.

Any suggestions?

Thanks in advance.

      Tamás