Handled EmailReference

This pull request handles the EmailReference pointer message which has been described in #4.
Sry, just noticed that you've been trying to get me to partake here, hence the delay.

I would vote for the option that comes with the largest probability of being able to deliver the message to the recipients inbox. If we know that mail servers has size limits, gzip seems like the best choice to me. But - I admit to not having followed all the details of your discussion, so I may be well off the mark here?