delaying received emails

Dear Colleagues, Received files with attachments more 1MB delayed more that 10 min depending how big is attachment. There is log caching from the Tracking center: in that case the attachment is 3 mb Jun 22 17:41:37 pmg postfix/smtpd[41279]: connect from smtp-out.abv.bg[194.153.145.80] Jun 22...