Payload Tab O365 Adapter
In BizTalk 2016 is possible to replace POP3 and SMTP Adapter with Office 365 Outlook Email adapters. For doing that is necessary to download and install Feature Pack 3 for BizTalk 2016.
Next are links:
For retrieve attach from email is necessary to configure the Payload tab inside the Office 365 Outlook Email:
The Office 365 Outlook Email adapters present in Feature Pack 3 for BizTalk 2016 is a lite version so don't have these feature expose by Payload tabs. If is necessary to get attach from email is mandatory to migrate to BizTalk 2020.