MTA - Can't relay from external network for external domain

Question

Hi All, 
 Im using XG310, and we have zimbra mail, we can send email to internal mail account from inside network and outside network, but we can't send mail to external domain from outside network 
 I have been trying to do all possibilities on firewall rule using Business Application rule, I'm using the email server (SMTP) and Email client (POP and IMAP) 
 we got error on mobile device using smtp (587) "Couldn't verify account, server does not support authentication. " 
 and also we using certain dedicated ip for sending as spf record 
 Can someone please point me in the right direction? 
 Thanks in advance 
 Andika

LuCar Toni · Answer

I am struggling with the explanation of your issue. 
 You want to use XG as a SMTP Auth Relay? This is not supported. 
 we got error on mobile device using smtp (587) "Couldn't verify account, server does not support authentication. " 
 The Mobile Device tries to do: https://en.wikipedia.org/wiki/SMTP_Authentication 
 XG Cannot perform it. 
 You have to think about another approach. And i would highly recommend to do that.. XG Should not be used as a auth relay for mobile devices. 
 The mobile devices should use the exchange for example with active sync. 
 Not a direct connection to XG and use it as a relay. Because you have no control about, what the device is doing. Just credentials and you could send what ever you want over XG in the name of your company. And who is logging it?