Message Not Delivered

I have a site that uses a custom domain BUT does NOT use its Mail. I use GSuite for email. It's MX record goes to Gsuite despite its domain being setup for FTH.

So instead, I have Gsuite set up email aliases, for example, sending an email to contact@dctm.org goes to contact-7864@toastmastersclubs.org.

OK. I send an email from an outside gmail address, and I get:

Your message has not been delivered to any of the original recipients because it has a destination club email address (contact-7864@toastmastersclubs.org) that is not part of the To or CC fields.

Please note: We do not support the use of BCC. If you are sending to an email address on this server using BCC please re-address using To or CC and try again.

So... I sent an email to the contact-7864 address and it works.

We warned you when you started down this road results could be weird and wonderful. We will not spend our time debugging it.

Email to contact have to to be contact-nnnnn@ or is there is a custom domain using FTH mail contact@domain in the To: The mail server wont accept mail to a domain when it is not setup to process that domain.