My Friends... I have a here interesting situation to decide... I have two domains in the network... being that one of them is a PDC in NT4 and Exchange5.5. The other is a domain Win2003 and some sub-domain (child).... I obtained to create one trust relation between the two domains, and of this form I can change the Primary Account of e-mails the Exchange5.5, of form that the users of the domain Win2003 can use its password of the net to login in e-mail of the domain NT... This trust in the domain Win2003 was as "external"... Then I tried you create one trust between the NT and the sub-domain of the Win2003...The NT accepted, but it only accepted to create as "Realm" in the sub-domain (This is currect?)... In the hour to change the Primary Account of the account of email of the NT for the sub-domain of the Win2003, it he arrives to see the users of the sub-domain and I obtain adds it as Primary Account, but he gives an error: "No mapping between account names and security IDs was done" Microsoft Windows NT ID no: 0xc0020534 Then I obtain to make this between the domain NT and Win2003, but not I obtain between the dominio NT and the subdominio of the Win2003. it has some form to decide this? Tks Alysson Dias Rio de Janeiro - Brazil