That would be true of most mail servers and accounts that impose quota's. Unless you have a really small account quota this shouldn't really be a problem because as an administrator you would have to be a bit of a glutton for punishment to accept emails over 15mb in size (Zimbra defaults at about 10mb I think).
I should point out though when I got my 111mb attachment I wasn't the mail admin although I would have probably hated to have been him at the time....111mb was probably a fair substantial portion of the disk!
