PHPmailer, local domains and externals mail servers

(I placed this post into "usage" forum, if one admin can delete that post... thanks, because i cannot do it).

My problem: i have installed several domains with several wordpress
installations, each wordpress has one contact form for each domain ([email protected]),
my problem: phpmail try to send (with postfix) to our local server...
so messages "dissapear", this problem was solved in iscp with this:

"Postfix doesn't check DNS settings when a domain is configured as
local. Hence, you have to remove the domain from the local (virtual)
domains table, by commenting it in files "/etc/postfix/ispcp/domains"
and "/etc/ispcp/postfix/working/domains". Next, "recompile" the table
with "postmap /etc/postfix/ispcp/domains" and restart postfix
("/etc/init.d/postfix restart")"

I tried this... no result

If i try to add correct smtp server in "external server", no works (phpmailer doesnt identify correctly to smtp)

¿how can solve this REALLY BIG trouble??? (really only need is that postfix works in all domains as foreign domains)

Thanks for close the thread in "usage" forum, as i can see, is not possible to delete one post.
If someone knows one solution for my trouble...(you see, thread is not closed now).

Thanks!