• SharePoint in Office 365
• Exchange Online (Office 365)
• Skype for Business
• Office 365 Security
• Office 365 Users
• Office 365: OneDrive for Business

Unsorted:

• Sending email from printers and scanners
• Office 2016 doesn't connect to Exchange 2007 (eg on SBS 2008) - see Exchange Server Supportability Matrix
• UPN suffix for Office 365
• Azure AD Connect (DirSync replacement)
• Add Email Alias (Secondary Email) to Office 365 Account that has AD DirSync
• Change Error Report Email Destination for DirSync
• Migrating from Exchange to Office 365
• Remove deleted users in Office 365
• Office 365 Licenses
• Office Deployment Tool for Click To Run
• Configuring Outlook for Office 365
• Office 365 PowerShell
• Microsoft recommends "setting passwords to never expire for service accounts, such as the account used for Active Directory synchronisation" (or see Office 365 PowerShell for the commands to change all passwords to never expire, if you're using DirSync and would prefer to manage expiries in AD)
• How to set up a multifunction device or application to send email using Office 365 (including instructions to set up an SMTP relay in IIS)
• Change logon name: Set-Mailbox OLDUSERNAME@DOMAIN.COM -MicrosoftOnlineServicesID NEW.USERNAME@DOMAIN.COM