I am using courier-imap 4.0.3 and 4.1 (on different servers). In both cases I am encountering a problem with mail that arrives with the following header:

X-Priority: normal

IMAP just reports an error to the web client and refuses to open the mailbox (unfortunately, I don't have access to the client code so I can only look at this problem from the perspective of the IMAP server) If I change the value from 'normal' to a numeric, such as '1', everything works fine. These mails are only arriving from a few identified sites. I want to contact them and explain the difficulty we are having, but I am not certain that the problem is not on our end and I don't want to waste their time or dilute our reputation. Can somebody point me to some comprehensive documentation on this header (an RFC?)? Google has so far failed me. Or better yet an explanation of the circumstances I am witnessing and the correct resolution, whether at our end or the sending sites?

Thanks

mike