Trying to configure email using custom gateway for the first time (I've configured a bunch for gmail/ms365 before, no problems).
So this customer needs to be able to send from onprem via sophos, I've verified the domain and added the mailboxes (aad directory sync).
Added their wan ip (added to spf) as outbound custom gateway.
Tried sending test email via telnet, when that didn't work I tried hmailserver.
Sophos says:
554 5.7.1 Service unavailable; Unverified Client host [reverse dns of host] blocked using uri.ire2.sophosxl.com
What may I be missing here?