I am trying to block a type of X-Mailer by adding a discard in the postfix_header_checks.in. I have included the contents that I am adding.

# Following is a list of known mass mailer programs.
/^X-Mailer: The Bat / DISCARD

After doing a postfix reload, I am reciveing the following message.

postmap: warning: /opt/zimbra/conf/postfix_header_checks.Sv7789, line 6:
record is in "key: value" format; is this an alias file?
postfix/postfix-script: refreshing the Postfix mail system

Line 6 is the X-Mailer line that I have added. Should I have added this in a different format?

Thanks for any help,