I really like using Signals by Hubspot for “read receipts” that work in Gmail/Google Apps mail.  You get 200…

I really like using Signals by Hubspot for “read receipts” that work in Gmail/Google Apps mail.  You get 200 notifications per month on the free plan. Sign up through my link here and get your own free plan, plus I get a free month with mine.

Get it here: http://goo.gl/4fc5Dy