I recommend using a free service called SpyPig to include an invisible image in the email that will notify you when the email is opened (if images are enabled). I usually wait about 10 minutes after the notification and call the client or lead and ask them if they had a minute to check my email. They usually say something like "Yeah you have perfect timing, I just took a look at it..." It's a pretty slick little trick http://www.spypig.com/ Good luck!