If the email client you're using isn't made by Microsoft, your Office 365 password may not work.

DETAILS

• If it's an app that is made by Microsoft (Outlook 2016 for Mac, Outlook for iOS) you can use your Office 365 password.
• If it's a non-Microsoft app (Mail on iOS or macOS, Android native email app), you may need to make a unique app password for each one that you're using:
  
• Sign into your Office 365 account at https://login.microsoftonline.com.
• Once you've successfully signed in go to https://aka.ms/MFASetup. (Yes, it can be slow to load.)
• Click the App Password link at the top. NOTE: it looks like it’s part of the page title so it’s easy to overlook — see screen grab below.
  
  
  
  
• Click the Create button.
• Make a name to identify which device this is for.
• The newly generated password will appear on the following screen. NOTE: This is the only time it will appear so make a note of it in your records, otherwise you'll just need to make a new one.