I looked all over the Toshiba site and the latest version they show for an SES or IES is ver 4.617. The ver 5.063 is listed as being for the Stratagy MAS. Did you download the upgrade from the Toshiba site?

I also doen't see when that version was released. If it was close to when 4.617, then they might have removered it on that version same time. When they addded IMAP support, they removed Delete On Send because they thought they didn't need it anymore.

And you are right, best not to apply a fix made for ver 4.6 to ver 5.0.