[Dovecot] email message size limit

Simple question: I've discovered that dovecot's IMAP server imposes a ~5Mb limit on email message size. After a day of searching I cannot find the configuration parameter that governs this size. What is it? Or is there no such parameter?

Thanks in advance, Fred

P.S. ... and yes I've discovered the quota, Maildir++, etc plugin but that doesn't seem to be what I'm after.