The best. Better than the stock Gmail app for IMAP  because the minimum for that is 15 minutes. To me  that could spell disaster for time critical emails. 1&1 supports IMAP IDLE  which this BEAUTIFULLY supports! Gmail app... """"""""""""""""Duh...What's IMAP IDLE?"""""""""""""""" Whoop whoop MMFWCL to the developer!""
April 21 2016