Unable to download PDF attachments from iCloud email

Hi!

I am using Google Chrome, the latest version.

I receieve emails in iCloud email from senders A, B, C & D. They normally send PDF's.

When I open the emails, I can download the PDF's included in the emails from senders A, B & C.

For some reasons, I can't download the PDF's from sender D. What I have to do is FWD his emails to my Gmail and download the attachments in Gmail.

Any idea how I can fix this problem with sender D?

Thank you.

[Re-Titled by Moderator]

Original Title: Downloading attachments in iCloud email