Microsoft announced in Spetember of last year that they would be disabling Auto forwarding for emails at it risks hackers gaining access to users data by manipulating the forwarding settings. Microsoft gave instructions on how to disable this https://support.microsoft.com/en-us/office/stop-auto-forwarding-emails-in-microsoft-365-f9d693ba-5c78-47c0-b156-8e461e062aa7
However many companies ignored or overlooked Microsoft's advice and then noticed their auto-forward email bouncing with NDR's as shown below.
to continuing the email forwarding feature customers were advised to enable the email spam policy for auto forwarding in O365 and scope auto forwarding to a user or group on requirement rather tan having it enabled for the whole tenant, even though this is still possible to do.
To change the outbound spam protections settings, contact your Microsoft 365 administrator and ask them to allow automatic external forwarding for any mailboxes you want to use with Help Scout. I have created the below steps to help your administrators find and change the outbound spam protection policy that is blocking your forward.
To enable automatic forwarding for all mailboxes.
Log in to your Office 365 Security & Compliance portal for Microsoft 365 and choose Threat management > Anti-spam or head directly to the Anti-spam settings page here: https://protection.office.com/antispam
Click the down arrow next to Outbound spam filter policy (always ON) and click the Edit policy button.
Click the down arrow next to Automatic forwarding, then choose On - Forwarding is enabled from the dropdown. Click Save.
Note this allows automatic forwarding of all mailboxes but its also possible to enable forwarding for individual users and groups.