ok, thats a good idea, if youre not supposed to store the email permanently on a mobile device... you won't, thats common sense
you still have 2 options:
retain a url to a webbased email service: thats easy, if the web service is already available
store the emails into files...
[thinking aloud] write the entire email into a file with a string identifier
store the identifier into the database
maybe create a sdcard for more storage...
you will even be able to store binary data
give it a try