[3.1b] Invalid regular expression in helo_access
Jun 17 10:05:04 postfix/smtpd[21553]: warning: regexp map /etc/postfix/helo_access, line 19: Invalid preceding regular expression
The only uncommented line is
/^{myhostname}$/ REJECT
changing it to
/^{$myhostname}$/ REJECT
seems to fix the warning