Hi, I was wondering if anybody can help me with my situation. I'm fairly new to Zimbra and the Linux environment.

I've managed to successfully implement Zimbra into our company network and so far all is working well, except for people sending emails to external addresses from an external network. for example, an employee working from home wishing to send an email to a GMAIL account will fail to smtp error 554 - transaction failed.

we use the mail server to pop and smtp to retrieve and send emails respectively on the same address:
eg. pop3 server: email.server.com.au
smtp server: email.server.com.au

so far:
local users within company network: can send/receive emails to and from internal and external addresses using outlook or web client. absolutely no problems within internal network what so ever.

but
external users outside company network: can only retrieve emails from internal and external addresses using outlook. they can send emails to internal addresses but not external addresses.
they have no issues with the web client from external network, however they prefer to use outlook.

bandaid fixes so far:
-i have advised home users to use their ISP's mail server for outgoing mail.
-i've added their external ip address subnet to trusted networks list
(eg 203.171.58.0/24 or 220.0.0.0/8)

i need help finding a permenant fix because the first bandaid solution is annoying when you have to keep changing smtp addresses everytime you are in a different location.
and the second solution leaves the mail server open to spammers.

have i missed a setting?

kind regards,
AW