Emails sent from Zoho to clients using Outlook is crashing their outlook

Emails sent from Zoho to clients using Outlook is crashing their outlook

I have now had multiple clients inform me that the emails we send with quotes included are crashing their outlook when they click to open the email. They then re-open outlook and they are able to open and view the email. But this happens every time they receive an email quote from us through Zoho.