Peter, David,
thanks to your quick responses and davids magick (coding) it's solved: the provided pre-release candidate (only changing MERCURYP a bit) now works nearly flawless. The POP3-Server is a lot faster than it was in 4.52...
Thanks a lot to everyone - keep on that great work! (I think the "big" competitors never can keep up with that flexibility and reaction-time...)
Kindest Regards!
P.S.: Nils: Thanks to David's bugfix there's no more need to work around anymore - thank you anyways...