By default, no virtusertable entries are defined and the virtusertable file looks something like the following:
# Simply add the virtual email address
# and the real email address
# it should be mapped to.
# The virtual email address can be a full
# email address or a hostname.
# If it is a hostname then mail to
# that hostname will be sent to the real
# email address if none of
# the full email addresses don't match.
# This keeps mail for a virtual
# sub-hosted domain from bouncing.
#
# Here are some examples:
#
# (lines beginning with "#" are comments;
# I love comments)
#Virtual Email Address Real Email Address
#---------------------- ------------------
# webmaster@virtual1.com user@isp.com
# user@virtual1.com localuser1
# virtual1.com user@isp.com
## Note: "Unknown User" mail to virtual1.com
## goes to user@isp.com
#
# webmaster@virtual2.com localuser2
# user@virtual2.com someuser@aol.com
# virtual2.com localuser2
#
Like the /etc/mail/aliases file, the /etc/mail/virtusertable file can contain lines that start with a # sign. Such lines act as comments and are ignored.