Emails sent to my group address are bouncing back, why?

Emails sent to my group address are bouncing back, why?

Hello,

Hoping for some help; I can't make headway on my own and my support requests haven't led to a resolution.

I have two users - myself - amanda<at>sqftnc<dot>com, and another member of my org - cassy<at>sqftnc<dot>com. I set up a public group of which Cassy and I are both members: office<at>sqftnc<dot>com

Mail sent to office<at>sqftnc<dot>com bounces back with this notice:
.........................................................................

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain sqftnc.com by smtp.secureserver.net . [68.178.213.37 ].

The error that the other server returned was:
550 5.1.1 < office@sqftnc.com > Recipient not found.  < http://x.co/irbounce >

............................................................

Zoho support is repeatedly telling me to confirm office<at>, but since it's a group address I'm not aware of a way to do that.

Can anyone help me? Thanks!