This error comes from c-client itself. What version
you have compiled PHP with?

I'm not sure; I will check tomorrow when I have access to the server and post another followup.
The problem, isn't the error, though. The problem is that putting the @ infront of imap_msgno() and imap_header() _should_ supress the error output, and it is not. The error should not be appearing, but it is.

Afaik this is related to how the current error handling in the ext/imap extension is implemented.

Can you try settings error_reporting(E_NONE); _before_ you call the function in question and see if it does not output the error message? 

Putting error_reporting(0) supresses the errors. I can use this temporarially, but it's not an effective long-term solution.

E_NONE does not seem to be defined! Should I file a separate bug for this?

E_NONE just doesn't exist :)

Actually, it's slightly more complex than I thought:

if I bracket the line giving the errors with

$__old_err = error_reporting(0);
...
error_reporting($__old_err);

I still get the error output. If, however, I leave error_reporting disabled through script completion, the errors are supressed.

Some additional testing reveals that if I simply put an error_reporting(0) at the very end of the script, then the errors are not displayed, regardless of there being @'s in fromt of imap_header() and/or imap_msgno(). But other warnings (like accessing undefined variables) are still thrown.

Sorry for the E_NONE ;-)

Chances are that the error goes to output only on script shutdown ... hmm ...

Will not set this to feedback this time as this should be investiged (I will if I find the time). Remind me that we've similar bug reports for this behaviour.

This should be fixed in PHP 4.2.1 and properly fixed in PHP 4.2.2-dev found here:

http://snaps.php.net/php4-STABLE-latest.tar.gz