you/your users would not get any warnings/messages that a mail has been queued for a certain time, and getting rejected with a temporary failure code 4xx
check /var/lib/pmg/templates/main.cf.in:
Code:
[% IF pmg.mail.dwarning %]
delay_warning_time = [% pmg.mail.dwarning %]h
[% END %]
if it's 0 the if evaluates to false and no delay_warning_time is set in the postfix config