I have no idea whether this helps you eliminate any specific issues or not, but I use EasySync Pro 4.2 with VersaMail, no problems. However, this is syng'ing with my R5 app, not my ND6 app. The version of VersaMail I'm using is 1.5.1, and it's on a very old Palm which doesn't come with any email "out of the box" (m100).
Cheers
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http://www.benpoole.com