Postfwd1 counts the size of a message only once even if the number
of recipients is > 1. For example
May 15 20:21:48 iac postfix/qmgr[5056]: CB2141329:
from=<sylvia@example.com>, size=12229263, nrcpt=69 (queue active)
will add only 12229263 for a rule like
id=QUOTA ; action=size(sasl_username/200000000/86400/WARN ...)
It seems that in /usr/sbin/postfwd1 in %postfwd_actions at the line
my($rcount) = ( ($mycmd =~ /^size/) ? $request{size} :
(($mycmd =~ /^rcpt/) ? $request{recipient_count} : 1 ) );
recipient_count is ignored, i.e. it is always assumed to be 1 for
($mycmd =~ /^size/).