Let us look at the changes that have been introduced in 2020 Release wave 2, with regards to the file attachments in Email.
Enable early access to 2020 release wave 2
Check other posts on Release 2020 Wave 2
Clicking on New Attachment button will,
open Manage Attachment dialog box in 2020 Release wave 1, wherein we need to click on Choose file to open the open file dialog box.
In 2020 Release wave 2, it will open the open file dialog box directly.
For the attached file, we have only the Delete option available in 2020 Release wave 1.
In 2020 Release wave 2, we have Preview, Download along with Delete option.
Clicking on Preview will open the attachment preview dialog box as shown below.
For attachment of type pdf, we get the below message
We do not see the preview option available for word document or text file.
Dynamics 365 2020 release wave 2 – https://docs.microsoft.com/en-us/dynamics365-release-plan/2020wave2/
Hope it helps..