Name
smtpd_expansion_filter
Possible values:
characters
Default:
(see example)
List of characters that are allowed in macro expansion by the
SMTP server.
Example:
smtpd_expansion_filter = \t\40!"#$%&'( )*+,-./0123456789:;<=>?@ \
ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~