[CNB] DKIMHook should also validate mail from

[chibenwa]

On port 25 we wishes that only mails originating from the platform (either authenticated OR DKIM signed) uses FROM local address in their mail headers.

GIVEN [email protected]
WHEN [email protected] sends a mail to a local user
AND uses `MAIL FROM: <[email protected]>` in the envelope
AND sets `From: [email protected]`
THEN the SMTP transaction on port 25 gets rejected as the mail is not DKIM signed

Note: legitimate use of local from from external sender is:

GIVEN [email protected] redirects mails to [email protected]
WHEN [email protected] sends a mail to [email protected]
THEN orange.fr will send us a mail using a local From but we shall accept it as the DKIM is valid...

What to do

Modify DKIMHook.DKIMCheckNeeded.onlyForSenderDomain in order to apply if the from of the envelope is matching the domain OR the *header from is matching the specified domain.

Special care needs to be taken in order to handle invalid header from (second clause is skept in case of error).

We need both unit and integration tests for this.