I recently downloaded MusicXML so I could convert Sibelius files and email them to someone who wants to open them using Finale.

Problem is, the converted files don't retain any articulation, accidentals or correct note beamings etc.

Any ideas how I can get around this? Would it be best to simply send them as PDFs and hope he can scan them?

Help!

Maybe try importing into MuseScore, to see if you can pin the problem down to either Sibelius or Finale? If that doesn't help, the Finale mailing list is frequented by lots of knowledgeable folk.

However, don't be surprised if the eventual answer is that some things (custom beamings, for example) cannot be preserved, and put it down to an annoying lesson in how proprietary file formats can cause problems with trying to share information.