how do you keep all@ away from external users
 

HI all
I have a pig problem in my send mail server I have a lot of users, I make an alias for all users all@mydomain.com
how can I prevent receiving maill from other domain to all@mydomain.com
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It depends on the mail server software. Somewhere in its documentation there should be mentioned a mathod to set up white and black lists (mail accepted and not accepted). That's what you need. Which mail server do you have?

I'm using send mail with imap