I upgrade to 4.5.3 last night which went ok I did this so I could use the Tusted Network. I entered a specific address 192.168.202.37 which stopped me sending mail from the webclient using an email client it was fine. Then tried 192.168.202.0/8 this stop postfix send mail completely, if you telnet'd to port 25 it did not come with a 220 message and just disconnected after a while.

I then clear the Trusted Network field and save again( from global mta config), this produced the following in zmmtaconfig:
DO: /opt/zimbra/postfix/sbin/postconf -e content_filter=''
DO: /opt/zimbra/postfix/sbin/postconf -e content_filter='smtp-amavis:[127.0.0.1]:10024'
DO: /opt/zimbra/postfix/sbin/postconf -e smtpd_use_tls='yes'
DO: /opt/zimbra/postfix/sbin/postconf -e mailbox_size_limit='0'
DO: /opt/zimbra/postfix/sbin/postconf -e smtpd_reject_unlisted_recipient='no'

I then had a look in /opt/zimbra/postfix/conf/main.cf which still had the entry mynetworks = 192.168.202.0/8
which I deleted and restarted the service and everything looks ok.

In the mailbox.log you got the following error when I first had a specific address in the trusted network field:

Caused by: javax.mail.SendFailedException: Invalid Addresses;
nested exception is:
com.sun.mail.smtp.SMTPAddressFailedException: 554 <nickteagle@gmail.com>: Relay access denied

at com.sun.mail.smtp.SMTPTransport.rcptTo(SMTPTranspo rt.java:1196)
at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTr ansport.java:584)
at javax.mail.Transport.send0(Transport.java:169)
at javax.mail.Transport.send(Transport.java:98)
at com.zimbra.cs.mailbox.MailSender.sendMessage(MailS ender.java:368)
at com.zimbra.cs.mailbox.MailSender.sendMimeMessage(M ailSender.java:248)