It seems to me that any new email items are updated probably once in 15-20 minutes. Unlike my when using my Google Mail account, it looks that my Microsoft Outlook 365 folders are not automatically updated with incoming email messages.
Here’s a question we got from a reader about her Microsoft Outlook client not showing new incoming emails automatically:
Applicable to: Outlook 365, 2019, 2016, 2013 Windows and macOS
