Ever since I'm using Zoho Mail integrated with Gmail, I'm having problems with some failed email deliveries.

The error email I've got is:

Your message couldn't be delivered because the group you're sending to needs to know who you are before it will accept your message.

To fix this problem, ask the email admin for the group to configure the group to accept messages from you.

For Email Administrators
This error occurs when the group is configured to reject email from senders outside of the group's organization. To fix the issue, the recipient's email admin must either add the sender's address to the group's list of allowed senders or they must select the group's delivery management option that allows senders both inside and outside of their organization to send email to it.

For more information and instructions on how to do this, see NDR status code 5.7.133 in Office 365 and Exchange Online.

Can you help please?

Regards

Bruno