[Dovecot] procmail -> deliver: file too large

I am using procmail with deliver as recommended on the wiki to send mail snagged by SpamAssassin straight to a spam folder. It seemed to be working fine, but now I'm finding messages like this:

Sep 17 12:13:47 hosty deliver(whoey): write() failed with mbox file /var/mail/whoey: File too large

I don't think this is a setrlimit problem -- the host operating system is OpenBSD 4.0. My dovecot version is 1.0.13. Is there a maximum size used by deliver? Or is this a procmail problem? It looks like the message is coming from deliver.

I don't think this is a postfix problem -- my max message size 33M in postfix.

-Thanks, Jim