modern days aliases

Asuming we have on a mail server(that hosts some external aliases, like has an alias for, which is hosted on a different server, probably on a different mail provider. Typically when a mail is sent to, it’s sender’s mail server sends the mail to the MX which hosts the mail is accepted, but being an alias the MX tries to send it again to

This didn’t used to be a problem few years back when methods like SPF or Sender-ID didn’t existed and the server hosting the email would not check if the server identifying as the original sender’s mail server is legit or not.

Sadly, nowadays this wouldn’t work, the MX would reject the mail just because the MX is not the MX for the original sender.

So, the mail server needs to alter this email so that’s MX believes the mail comes from

In Postfix this type of configuration is quite simple. The first thing to set the virtual_alias_maps table and put into it as an alias to a local account, something like user1

The next step is to modify the local alias map, typically situated in the file /etc/aliases and put something like:

user1:  "|/opt/redirector"

Then we need to create the /opt/redirector script, which has only two lines:

/usr/sbin/sendmail -bm -f $1 $2

the script needs to be executed

chmod +x /opt/redirector

some database update

postmap /etc/postfix/virtualnewaliases

restart postfix(probably not really necessary) and voila!


Image credits.