If you are using the pre-installed email app on the Samsung Galaxy S8, the following message may appear on the screen when downloading an email attachment: "Warning - Before you can download the attachment, you must download the email". At this point you won't be able to download the appendix.
The reason for this is explained here:
Display the email on the Samsung Galaxy S8 and scroll to the bottom of the email. This automatically reloads the content of the e-mail via W-Lan or the mobile data connection. This also includes the attachment of the e-mail.
This can then be downloaded without any problems within the Android e-mail app. Depending on the size of the attachment, this may take a little time to download.
You now know the cause of the warning message "Warning - Before you can download the attachment, you need to download the email" on the Samsung Galaxy S8 and also how to download it anyway.