Re: sender rewrining advice

I have there, access:
to:test@example.com    RELAY

 Do you also have a corresponding REJECT?
     to:@example.com    REJECT
 Without the REJECT I would expect Sendmail to accept the message as part of the relay-domains configuration.
 

Afaik it is currently like this, I have to put something in the access map to allow it through. Either test@example.com or @example.com on RELAY. Currently I am not using entries like @example.com any more.

host C, LOCAL is not in the spf records. I think external access is even blocked. I had spammers by passing spam blocking on the mx / host a and delivering directly to C

 SPF is about the connecting host.
 As such, GuerrillaMail.com will see host B as the connecting host and check it's IP against SPF records.
 Depending on your configuration, hosts A, B, and C may need to either have allow list entries or valid SPF information for each other.

I want to prevent as much as possible hosts that are allowed to send out email.