What if you use this instead:

$mbox = imap_open ("{localhost:110/pop3}INBOX", "user_id", "password");

(straight from the manual)

I thought I'd tried that already, but there must have been something else wrong when I did, because that fixed it. Thanks.  :-)

Side note... the reason I was trying it that way is because that's how NOCC v.0.92 (see http://sourceforge.net/projects/nocc/ )was successfully doing it.  I guess the syntax for imap_open isn't as flexible as it used to be.  My guess is that they've fixed NOCC in later versions and that's why no one else seems to be having this problem.

It's always a bummer when something that worked in a previous version of PHP stops working in the current one. But, as it stands, I guess that's not PHP's problem... this is a NOCC bug.  Unfortunately, I've got to go track down dozens of old NOCC installations (on lots of different servers) and fix the syntax to the way the current PHP wants to see it. :-(

Actually it's the imap library whose syntax did change, not PHP itself.

Additional note: I did some more experimenting and it turns out that the current PHP does NOT have a problem with this syntax:

imap_open("{hostname/pop3:110}INBOX", "userid", "password")

...which is the same syntax NOCC v.9.2 used with the exception that "pop3" is lower case.  

In summary, in previous versions of imap_open() the protocol specifier was not case sensitive.  Now it is.

Oops... I didn't see mfischer@php.net's comment.  Perhaps it is in the imap libary, but what's strange is I tried using the same library that I used with the prior PHP version and it still had a problem.