Consider using Email Archiver to create an archive of all your email before you upgrade to Mavericks. There have been reports of changes to Mail.app playing havoc with some people’s Mail installations, although my trove of 250,000 emails upgraded without a hitch to 10.9. If you make an archive with Email Archiver, the format of the archive is a simple folder structure filled with PDFs of all your emails and attachment folders where needed.  A feeling of peace of mind if you have years of correspondence trapped in Mail.app.

Mavericks comes with a few new features, one of which is tagging. 2.8.0 introduces Mavericks tagging on 10.9. On earlier systems, tags are created for the OpenMeta standard which works well for that. In addition Email Archiver sets up special attributes so searching for emails is easier and faster, whether you search in Email Archiver or the Finder.

Version 2.8.0 features a solution for the export problem – we have customers who use Email Archiver to make an folder of PDFs in order to send to someone for legal discovery, etc. The export command creates a new folder and makes all the PDFs it needs to – with the additional feature of creating duplicate PDFs where duplicate emails in the same folder are found. We have found that this is necessary for some legal work. Thanks to a customer for getting this feature in!