Ich habe mal die Logs durchforstet: All of April:

all mails: 1022761 (100,00%) bounces: 17558 (1,71%) non-bounces: 1005203 (98,28%)

spam all mails: 160579 (15,70% of all mails) spam bounces: 8101 (46,13% of all bounces) spam non-bounces: 152478 (15,16% of all non-bounces)

Also, Bounces sind schon spammiger, nämlich 3x so spammig wie nicht-Bounces.