Thank you for this information. I recently had to change my AppleID passwords... something I'd been meaning to do anyway. When I did I discovered that Indigo quit sending emails.
Going to AppleID at
http://support.apple.com/en-us/HT6186 solved the problem, creating a new app-specific-ID.
This is something that you don't do every day... maybe once every year or two if that. Specifically, what fixed my problem was to go to the link, click on "App-specific passwords" link, generate a link which I named "Indigo Email"... and Apple gave me an App-specific password that I was able to paste into the "SMTP password:" of Indigo's Email Preferences. This was actually a little counter-intuitive to me... app-specific password does not really say "EMAIL SPECIFIC PASSWORD" to me.... but that's where you paste it.