In QuickBooks, you can only send transactions through webmail or Outlook. Since you're accessing Outlook in Office 365, you'll have set it up as Webmail in the program.
Before you get started, please make sure to verify your webmail servers and port settings with your ISP. Additionally, webmail providers require users to enable their account settings for two-step verification.
Once you're ready, I'll show you how to do it:
Select Edit from the sidebar menu.
Go to Preferences.
Choose Send Forms.
Select Web Mail, then click Add.
From the Add EmailInfo window, enter the necessary information and then click OK.
Hit OK again to complete the process.
I also recommend reading this article to be guided in fixing common webmail password issues.
You can always find me here if you have any other concerns or concerns about emailing transactions in QuickBooks. I'll always have your back.