postfix/cleanup[25132]: warning: regexp map /usr/local/etc/postfix/sendercanonical, line 1: ignoring unrecognized request
postfix/cleanup[17182]: warning: regexp map /usr/local/etc/postfix/sendercanonical, line 1: unknown regexp option "c": skipping this rule
Pattern matching (inside the quotes) e.g. match all "/.+/" match a domain "/@domain\.com/i" match a user "/username/i"