Use SFOS as Mailrelay

Essentially UTM did it like SFOS does it today. Only the SMTP Auth Component is not the same (SFOS does not support SMTP Auth). 

How did you do it in UTM? Can you show us the configuration of UTM? Because essentially, if you did the host based relay approach, everybody can send an email with every Sender address in UTM. 

Hi Toni

Tanks for your reply. I will try to share the current configuration with you (I'm not proficient in UTM).

Email Protection -> SMTP ->

Global

• Profile Mode
• Listen Inferfaces = all

Routing

• Rout by: MX record

Relaying

• Host-based Relay = all Host entred which are allowed to send external Domains
• Content Svcan for ... = True

Advanced

• DKIM/DMARC configured for one Domain
• Advanced Settings --> Standard exepct specified Postmaster Address

SMTP Profiles

• Several Profiles which include our internal Domains (They should be routed to our M365 Tennant)

As i know, this should be the whole configuration, that is done for the Relaying. Hope this helps you to help me

"Host based Relay" did you enter here all the clients, you want to send emails from? Like Printers etc in UTM? 

Because that basically means, they can send EVERY Domain in UTM. 

No we only entered the Clients that should be able to send to external domains. Clients that should send only to internal.com, internal.org, etc. are not entered anywere.

Just to make sure: Are clients in the UTM entered in "Host based Relay" or not? 
Because UTM will not filter those clients. They can use the UTM for every kind of Emails. The UTM will not filter those Emails. 

I Double checked it be be compleltly sure. My current Client (example 192.168.100.140) is not entered in the Allowed Hosts/Networks List but I'm able to send Mails to an internal Domain:

I'm also tried to send to my private Mail address and the Sophos directly rejected the Mail

So there has to be a mechanism, which checks if its an internals domain or not. But I can't find any possibility to configure such setting.

I am not sure what you mean: Is your client now in Host based Relay or not? 

Can you share us a screenshot of this? 

My Client isn't in the List. Sharing a screenshot is because of data security a little bit difficult. Its a productive System with productive Systems including.

mymail@internal.com works but mymail@external.com diesn't work.