There are massive problems with these emails:

1. They are very sensitive to spam filters
2. If you alter the message to your friend on the referral website, no email gets sent!

I always email across my copy of the email to the person being referred. For weird reasons, if you forward the Amex email it tends to get through even if the original got spam-trapped.

If it hasn't arrived within a few hours, something has happened and you need to resend it.