Used to run it in OS 9. Then ran it in OS X and 9. Now running in OS X only. Not only have all of my attachments remained usable, v4 even fixed a problem that I caused long ago when I renamed my attachments folder. PM4 has its caveats but I have seen no other program that does all of what this one does (Applescript, IMAP [yes IMAP], spell checking, html, self repairing via cmd-opt at startup, and more attention to detail with so much less fat than the big email programs). The caveats have been minor over the years and slowly but surely ctm has been addressing them. This has been one of those great, rare shareware programs that makes a joke of the name 'Commercial'. Four stars for a great program, one held back for room to improve it still.