Can someone give a specific example/use case for SMTP commands
adaptation ?
How about these:
Use Case 1:
An MTA at a corporate gateway handles outgoing mail traffic.
In the "MAIL FROM:" command it gets the sender's email address.
Before replying to this command (allow/deny) it sends an OCP
request to an OPES service that checks in the corporate directory
service whether that employee is allowed to send mails to the
Internet. Depending on the OCP response the MTA replies in the
SMTP dialog with allow or deny.
Use Case 2:
The other way around.
The MTA sends OCP requests for all "RCPT TO:" commands for
incoming messages and asks the OPES service whether the
recipient exists and is allowed to receive email.
Use Case 3:
Sender validation via OPES. OPES service checks sender IP,
HELO command, resolves the sender address etc.
This may tell the MTA not to accept the message for delivery.
Could even be done asynchronously for some parts, i.e. sending
the OCP request after HELO or MAIL FROM and continuing to
handle recipients and to receive the mail body. The response
then needs to be there before the message gets finally accepted.
Regards
Martin