my postfix server should deliver mail for two domains: domainA.it and
domainA.com (yes, the domain name is the same, but the suffix change).
some site reports that the solution is in "relay_domains =
hash:/etc/postfix/relay_domains" and "transport_maps =
hash:/etc/postfix/transport" parameters in main.cf, using external text
files containing:

/etc/postfix/transport:
domainA.it smtp:x.x.x.x
domainA.com smtp:x.x.x.x

/etc/postfix/relay_domains
domainA.it OK
domainA.com OK

(x.x.x.x is the mailserver on the local network)

can anyone confirm this idea since i have found lots of different
solutions and i don't know which is the better and if this method is
correct.

Thanks,
paolino