Qmail and lotus domino

[Filippo Giunchedi]

hi all,
i've a qmail system on my network set up using life with qmail (great 
document!) the qmail's work is to accept connections for our lotus domino 
server (on NT) via smtp and then send out mail. but i've got a problem: 
some messages goes out without problems. some others bouce but the return 
path is incorrect so it bouce to the postmaster.
some ideas?
(i've to attach a copy with headers of messages?)

thanks in advance
filippo.