Is there any possibility to redirect / discard email of unknown users instead of sending it back to the sender with a rejection message that user is unknown?
I don't want to use any milter for this purpose or any sender validation tool. Have sendmail ability into it to do this?
The sendmail option you want is called LUSER_RELAY. To send all mail addressed to unknown users to "unknown" on the local system, you would put this line in your mc file:
define(
LUSER_RELAY',local:unknown')dnl
Once you have built a new sendmail.cf file you will have a line that specifies the destination for all email addressed to unknown users:
DLlocal:unknown
To never deal with the email, put a .forward file in the target user's home:
| /dev/null
