I have both a Gmail and an Outlook.com email account. Before the upgrade (?) to Marshmallow 6.01, the synching was great -- the calendar updated immediately. I have my calendar synched between my Outlook.com account, my Outlook client, and my phone, and it worked great. Ever since the switch to 6.01, the synching for both of my email accounts has been disabled, although I can pull down emails if I start my email client (K-9). However, the calendar will not synch at all. I am seriously thinking of downgrading back to Android 5.22; 6.01 has been a complete disaster, as far as I'm concerned.