FortiMail provides advanced, multi-layer protection against the full spectrum of email-borne threats
Article Id 193034
This article describes how to remove all hyperlinks in any received email unless the URL matches the URL exempt list.

1) From GUI, go to Profile -> Content -> Content and create a new 'Content Profile'.
2) Go to Content Disarm and Reconstruction, enable the HTML content and set it to 'Remove URLs'.

3) Apply the new content profile into the recipient policy accordingly.
4) Go to Profile -> Antispam -> URI Filter, create a new URI filter profile and select all Fortiguard Categories.

5) Go to System -> Fortiguard -> URI Protection -> URI Removal -> Category and change to new URL filter profile 'all' created in step 4.
6) Go to Security -> URL Exempt List -> Exempt and create a new URL Exempt. For this example, the URL is exempted like below.

All the URLs is removed except the URL because it is matched to URL exempt list.