OS Sierra Mail not showing Paper Clip icon for Attachments

Since I upgraded from El Capitan to OS Sierra, my Cox Pop e-mail accounts no longer show a Paper Clip icon when there is an attachment (or multiple attachments).

The attachments are coming through ok (i.e. you can open them), but you have to open each individual e-mail to actually see that there is an attachment.

My iCloud (IMAP) account still shows the Paper Clip icon when there are attachments. I have not changed any server settings since upgrading to OS Sierra.

The problem occurs on both my Mac Pro and my MacBook pro, so it is not isolated to a single machine.

Because I use my Mac for my business, I receive a lot of e-mails with attachments, at it is a huge pain to have to open each one to determine if there is an attachment.

Has anyone else found a solution to this problem?