Q:
Is there a way in which I can limit the size of messages that my qmail server will accept?
A:
Yes. You can create the file /var/qmail/control/databytes. Within this file you specify the maximum message size, in bytes, that your server will accept. For example, an entry of 10000000 would limit messages to 10MB. Anything over that size will be rejected by the server and the sender should get a bounce message stating that the message is over the allowed message size. The syntax of the file is easy. You simply put in the maximum number and nothing else. So for a limit of 10MB, you would create a file called /var/qmail/control/databytes and on the first line you would enter the number 10000000 and nothing else. Save the file and you're all done. You may want to restart qmail just to be sure it kicks in.