Clients can't email homestead/roundcube email.

Clients can no longer email the roundcube/homestead email we have. They get an error message back saying "the email account you tried to reach does no exist."

This doesn't make any sense. Can you please help us reestablish our email? We recently tried creating a good workspace account separately from homestead. It asked for a domain name so we provided the one we have with homestead. Since this happened we can no longer use homestead/roundcube email. how can we fix this?

Emma