In php3_imap_fetchheader (in the file functions/imap.c) a check is done to see that the passed-in message number is within the correct range of message numbers. However, it fails to take into account that the message number might actually be a UID if the flags parameter includes the FT_UID option. If FT_UID is set in the flags, the message number range check should be skipped.

The following change works:

old code:

    if (msgno->value.lval < 1) || (msgno->value.lval > imap_le_struct->imap_stream->nmsgs) {

new code:

    if (!(flags->value.lval & FT_UID) &&
        (msgno->value.lval < 1) || (msgno->value.lval > imap_le_struct->imap_stream->nmsgs)) {

NB A quick look at the PHP4 code indicates that this problem is resolved in a slightly different manner there. You may prefer the PHP4 fix rather than the one I've done.