Emails marked as phishing

Our client's website had a phishing page that was listed on http://www.phishtank.com/.

 

The offending website page was deleted, and the PhishTank no longer recognises the page (offending URL no longer exists).

 

If any Office 365 user sends an email that includes a link to this domain the email is marked as phishing (as shown below).

 

I'm out of ideas what to do next! Can the domain be whitelisted somewhere within Office 365?