Fortimail - Out of office emails to external contacts failure?

Hello everyone,

We're having an issue with out of office emails being denied when sent to external contacts. The reason given in the log is access control relay denied - I'm assuming because the sender of the out of office email is technically a blank address? Is there a way to workaround this yet? We're using Fortimail V6.0.4.

I found a link here: https://kb.fortinet.com/kb/documentLink.do?externalID=FD38125 but appears to not work for any Fortimail version upwards of 5.4

Thanks in advance!