man 5 virtual
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TABLE FORMAT
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user@domain address, address, ...
Mail for user@domain is redirected to address. This form has
the highest precedence.
user address, address, ...
Mail for user@site is redirected to address when site is equal
to $myorigin, when site is listed in $mydestination, or when it
is listed in $inet_interfaces or $proxy_interfaces.
This functionality overlaps with functionality of the local
aliases(5) database. The difference is that virtual mapping can
be applied to non-local addresses.
@domain address, address, ...
Mail for any user in domain is redirected to address. This form
has the lowest precedence.
In all the above forms, when address has the form @otherdomain, the
result is the same user in otherdomain. This works for the first
address in the expansion only.
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