I believe it was the most recent Update that added to the bottom of the Contact screen all the sales related documents with a check box next to them.
 
The help file doesn't mention them. I assume that if you check one or more off, that contact will get an email when the email option is selected. But exactly how, I don't know.
 
Does it work when you manually email? What about Auto-email? What if you do Auto-email and you already have a bunch of contacts that you've set up with letter codes in the Primary field and you enter that letter - do customers with one or the other option get them?
 
Just need some help here...
 
We went through all our contacts a while ago and added multiple contacts for all the different document types. Some of our customers have one person for Acks, one for PLs and another for Invoices. But many of our customers have the same contact for everything, so we had to add the same person multiple times with a different Primary letter for each document type. I see is as being a bit of a nightmare having to go through and change them all. Don't get me wrong - it seems like the new system is much better, but I can't just flip a switch to convert everyone...

Update.
 
There is NO difference to anything when these are checked off. The Auto Send feature simply does not work on PLs or Quotes.
 
I will submit a bug report.