I had an issue with the stock e-mail app not syncing properly with gmail. New e-mails would come in, but old ones that were read would not be marked as read. As such it had over 50 unread e-mails even though the gmail app or gmail website had 2 or 3.
I switched to K-9 Mail which works much better.
My Smartphone history with AT&T:
January 2005: Audiovox SMT5600 aka HTC Typhoon
June 2006: Cingular 8125 aka HTC Wizard
October 2007: AT&T Tilt aka HTC Kaiser
June 2009: AT&T Fuze aka HTC Raphael
November 2009: iPhone 3GS
July 2010: iPhone 4
October 2011: iPhone 4S
July 2012: Samsung Galaxy Nexus GSM/HSDPA+
May 2013: Samsung Galaxy S4 4G/LTE
April 2014: Samsung Galaxy S5 4G/LTE