Question: I want to capture a date on a SharePoint edit form.. then take that date and subtract that date from it to get a value for the number of days. Is this a complicated process or something simple? I'm not having much luck searching due to super secure (and unnecessary) security blocks.

Answer: 
If I had to guess, you have a webpage that has been compromised (which is what I think you suspect), and is being used to generate all the messages. The webpage probably accepts a FROM and a TO, without any validation.

If you start seeing these come in, as a test, start shutting off websites, until you see the attack stop.

Then, start the website back up, see if it continues. Then, I would start grepping that website location for files relating to email.
Most likely your server is configured to act as an email relay server, which allows anyone to send email that is in transit to your server for your server to send on (relay). Spammers do this to cover up the original origination point of the email.

The fix is to configure your server not to be a relay server. More background info here:

<http://en.wikipedia.org/wiki/Open_mail_relay>