How many mails would cause this error to show in Gmail "There are too many messages on the other server. Please delete some mail from..."

I'm downloading my email to a private Gmail account, from another POP3 server (SmarterMail Server 4.3). In Gmail I'm getting the error:

Error: Too many messages to download.Server returned error "There are too many messages on the other server. Please delete some mail from..."

So I can reduce the number of emails, but I don't know what maximum count I'm trying to hit.

Also using google on the error message only returns a few results from google sites, but non refer to an email count that would cause this error to start showing.