Why does email forwarding not work with external addresses?

I have tried to setup an internal email account which is meant to forward emails to an external account.

Under the account's mail options i have set "Mail should be: " to Forwarded and typed in the email address underneath. However, both with an external domain and the me.com domain it does not send the email. If i send an email directly from the accounts using my IMAP account the server has no problems sending the emails to the addresses.

The results of running sudo serveradmin command mail:command = getAutoForward is:

mail:<<id1>>:fwdAddress = "internalAccount1@internaldomain.com.au"

mail:<<id2>>:fwdAddress = "internalAccount2@internaldomain.com.au"

mail:<<id3>>:fwdAddress = "externalAccount1@me.com"

Is there sometime i'm missing?