Prior to ISMail Pro 2.3.61 (and ISMail 1.8.61), the INBOX message file used a *nix-like 'mbox' non-shareable format. Subsequent versions use a shareable format called 'mbx'.
Upgrades to ISMail Pro and ISMail do NOT automatically convert the INBOX format from 'mbox' to 'mbx'; the following conversion script must be run to do so.
Instructions for converting INBOX files to 'mbx' format:
The script should be re-run several times ('perl ...' line) to insure that all INBOX files have been converted, since an INBOX file being accessed while the script is running may not be converted.
Re-running the script will do no harm and will not affect INBOX files that have already been converted. The script will execute quickly if INBOX files are already in 'mbx' format.