Digital archives have to preserve not only the data formats, they also have to make sure that proper viewer technology is available in the future. For most paper like formats this is solved by PDF/A.
Email has replaced paper as the predominant format for business documents. The email protocol is standardized, but there is no standard email file format, instead email clients use a variety of formats. This raises many questions when it comes to archiving emails.
But there are questions beyond the format: an email is often related to other emails and it may be more useful to not only archive the email but also the context, i.e. the mailbox) from which it is archived.
A recently published paper (to which the PDF Association made many contributions) published by the University of Illinois at Urbana-Campaign discusses how PDF can be used to package and represent email.
There currently is no standard solution for interoperable email archival. This presentation attempts to provide an overview about the current state of discussions and developments in the field of interoperable email archival.