Size restriction for email attachment

[mareks]

Hello,
could you someone help me with restriction for email attachment. My problem is that I am not able to found settings for size of one attached file.
There is limit for email size (Ticket -> Core::PostMaster) but in case the one of the attached file is over 3MB email is delivered without attachment. I can see the mail in the post box with attachment so the problem is probably in the OTRS.
Thank for advices...