first of all excuse me for my english.
I'm a principiant of server zimbra, but for a my knowing that does not have many money and asked me for an implementation of a open source mail server, i have decided to install a Zimbra mail server. I have seen that it is
a fantastic system.
For many reason i have these situation:
The server periodically downloads messages from various external mail accounts, having different domains with the program FETCHMAIL and it forwards them to internal accounts on server zimbra, having all the same domain name. Up to here all it works perfectly; the problem is on sending email, because some messages are discarded from the adressee servers. I know that this action is made correctly , in order to contrast the phenomenon of spam mails, as the zimbra server has not a valid and registred hostname in internet.
So i have decided to configure Zimbra for using the ISP Server of my knowing, like an a smtp relay server for zimbra, but an other necessity is risen. An internal user wants use another smtp relay !
So i have found in internet the possibility of using the sender_dependent_relayhost_maps parameter of POSTFIX and thus making i could to forward mails to various smtp relay servers based on my internal account.
All this I do not succeed to make it to work because when a user sends an email it receives an error rcpto , from the external smtp relay.
My system is composed from linux fedore core 7 and Zimbra 5.0.10 and i have followed this guide:
Ok, so I went ahead and played around with postfix to see if I could get it to forward the mail the way I wanted. This seems like a really bad idea on a true multi-user system, since I'm pretty sure it would let anybody on my box send mail as me simply by specifying my email address in the smtp envelope.

There's an article on setting up two postfix instances to do smtp forwarding where the assumption is that each account on your box should be magically transformed into a single outgoing smtp account. I was able to glean a lot of info from it, but it wasn't quite what I wanted.

I've got postfix 2.4.5-3ubuntu1. Docs suggest that I would have had less trouble with the TLS configuration in 2.5, but I didn't really feel like recompiling it.
Set up sender-dependent relaying

Create sender_dependent_relayhost, which maps sender addresses to outgoing servers (don't forget postmap).

# cat > /etc/postfix/sender_dependent_relayhost
ryandjohnson@gmail.com [smtp.gmail.com]:25
ryan@innerfence.com [server1.gambitdesign.com]:25
# postmap sender_dependent_relayhost

Require TLS for the relays

Create smtp_tls_policy that requires TLS with valid certs for our relay hosts. In part this is necessary to guarantee that our passwords aren't sent in the clear, since gmail doesn't support anything else.

# cat > /etc/postfix/smtp_tls_policy
[smtp.gmail.com]:25 secure
[server1.gambitdesign.com]:25 secure
# postmap smtp_tls_policy

Set up passwords

Create sasl_password that configures your username/password for each host.

# cat > /etc/postfix/sasl_password
[smtp.gmail.com]:25 ryandjohnson@gmail.com:nopaste
[server1.gambitdesign.com]:25 ryan@innerfence.com:nopaste
# chmod 600 sasl_password
# postmap sasl_password

Fix TLS certificate validation

We need to link in the openssl roots and take the smtp client process out of chroot. This kind of sucks, but I didn't really see any other way to do it.

# ln -s /etc/ssl/certs /etc/postfix/certs
# $EDITOR /etc/postfix/master.cf
-smtp unix - - n - - smtp
+smtp unix - - - - - smtp

Hook it all up in main.cf

# $EDITOR /etc/postfix/main.cf
+# Relay according to the sender address
+sender_dependent_relayhost_maps = hash:/etc/postfix/sender_dependent_relayhost
+# Turn on TLS for the smtp *client* (for relaying)
+smtp_tls_CApath = /etc/postfix/certs
+smtp_tls_policy_maps = hash:/etc/postfix/smtp_tls_policy
smtp_tls_session_cache_database = btree:${queue_directory}/smtp_scache

+# Use SASL authentication over smtp *client* (for relaying)
+smtp_sasl_auth_enable = yes
+smtp_sasl_password_maps = hash:/etc/postfix/sasl_password
+# allow plaintext (over TLS)
+smtp_sasl_security_options = noanonymous

Fire it up, test it out

# postfix reload
# sendmail -f ryandjohnson@gmail.com -t ryan@innerfence.com
From: ryandjohnson@gmail.com
To: ryan@innerfence.com
Subject: test message

The quick brown fox jumps over the lazy dog.
# tail /var/log/mail.log

Be sure when you're testing it you view all the headers on the mail you receive, to ensure that you get domain key signatures, SPF passes, and all the other modern goodness which is really why you want to do it.
Exists someone that can help me?