I've assembled lists of sites where you can look for information and help on APIs dealing with developing applications against Exchange and Outlook.
Messaging Development training:
Exchange Server development
https://msdn.microsoft.com/en-us/library/office/dn820100
Welcome to the Outlook 2013 developer reference
https://msdn.microsoft.com/en-us/library/office/ee861520.aspx
Channel 9
https://channel9.msdn.com/
This is Microsoft's video based training site. It covers a broad range of developer topics including messaging APIs.
Developer Support Team blogs:
Developer Support Messaging Team
https://blogs.msdn.com/tags/DevMsgTeam/
EMEA Developer Support for Messaging Team Blog
https://blogs.msdn.com/b/emeamsgdev/
Exchange product team blogs:
Exchange Dev Blog
https://blogs.msdn.com/b/exchangedev/
Exchange Team Blog
https://blogs.technet.com/b/exchange/
Outlook development:
Office Developer Documentation
https://msdn.microsoft.com/en-US/office/aa905340
Office client development
https://msdn.microsoft.com/en-us/library/office/dn833103.aspx
Microsoft MVPs:
Glen's Exchange Dev Blog
https://gsexdev.blogspot.com/
This is one of my favorite sites for Powershell scripts.
Glen Scale's Exchagne Column
https://www.outlookexchange.com/articles/glenscales/
Slipstick
https://www.slipstick.com/
Forums:
EWS discussion on stackoverflow
https://stackoverflow.com/questions/tagged/ews https://stackoverflow.com/questions/tagged/exchange-server
https://stackoverflow.com/questions/tagged/outlook
Exchange development forums
https://social.msdn.microsoft.com/Forums/office/en-US/home?category=exchangeserver
Getting Support:
Get support - Exchange
https://support2.microsoft.com/oas/default.aspx?LN=en-us&gprid=730&x=13&y=7&st=1&wfxredirect=1&sd=gn
Support - All products
https://support.microsoft.com/en-us/allproducts
Other:
OutlookCode
hthttps://www.outlookcode.com/