Is it possible that zimbra/postfix relay a mta host for only some recipient domains?

Hello,

In past 2 weeks, i got emails sending problem.

All my zimbra servers verison is Release 8.0.2_GA_5569.RHEL6_64_20121210115059
Server no.1 (mail.mydomain.com located in Thailand ISP) got problem that it can't send a big size email (over about 5MB.) to @yahoo.com (email size below 5MB. was sent fine)

Error Log :
dsn=4.4.2, status=deferred (lost connection with mta6.am0.yahoodns.net[67.195.168.230] while sending message body)

so I've set a new zimbra just for MTA server in USA (mta.mydomain.com) server no.2

and set zimbraMtaRelayHost on server mail.mydomain.com to mta.mydomain.com , Now can send emails to yahoo.com any size :o
BUT :( server no.2 (mta.mydomain.com) have problems sending emails to some domains that mail servers located in Thailand too. (most of errors are timeout errors)

Is it possible that zimbra/postfix relay a mta host for only some recipient's domains?
example :
@yahoo.com @yahoo.co.uk @yahoo.co.th relay to mta.mydomain.com
@gmail.com @hotmail.com relay to mta2.mydomain.com
other recipient's domains send directly from server no.1 mail.mydomain.com

Thank you very much.