I disagree with the other answers in that I would not include an image (or full text), of any recent personal correspondence in a database accessible to others, without their express permission. When someone writes you an email they usually do not expect you to post it on the internet for all to see. Whether or not the email contains sensitive information, it would be prudent to ask the person who wrote the email whether you would be okay to circulate the email online.
I have corresponded with many people regarding my family tree over the years, and it annoys me when I see the full text of a private email written by me posted on RootsWeb or Ancestry or somewhere. This has happened to me multiple times.
You don't need to include the full email, but certainly cite your source – e.g. something like:
Personal correspondence (email) from John Smith, Gwent Crematorium, 14 Apr
That's all you need. Include the details of the email (i.e. a summary of pertinent details) in the citation transcription or other notes, if needed. No real need to include an email address – they change frequently.
Someone can now track down that same source, very easily, if they want further details. They just need to contact Gwent Crematorium, and ask for John Smith.
There are many different citation style guides, but as long as you include enough information for someone to find the same source, you have done your job. If you were publishing in a journal, there might be a specific format preferred, but this is your family tree. Personally I find it very annoying when citations are padded with unnecessary information.