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.