When setting up forwarding from Microsoft 365 (formerly referred to as Office 365) to Help Scout, you may need to take an additional step to complete the process. Some Microsoft 365 accounts default to block automatic email forwarding as part of their outbound spam protection. If external forwarding is disabled for your Microsoft 365 account, you will see a specific bounce message in your inbox at Microsoft 365 after attempting to set up forwarding to Help Scout. The text of the bounce will include this line:
550 5.7.520 Access denied, Your organization does not allow external forwarding. Please contact your administrator for further assistance. AS(7555)
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. We’ve created this guide to help your administrators find and change the outbound spam protection policy that is blocking your forward.
For Microsoft 365 Administrators
Configuring external email forwarding in Microsoft 365 is Microsoft’s documentation of the security features they’ve put in place. Below you will find a step-by-step guide for changing the specific portion of the automatic forwarding settings needed to work with Help Scout.
If your Microsoft 365 account was purchased through GoDaddy, they have their own method for changing these settings as outlined in their help here: Microsoft 365 from GoDaddy Help: Enable external email forwarding
You may choose to enable automatic forwarding for all mailboxes in your Microsoft 365 account, or enable it only for the mailboxes you’re forwarding to Help Scout. Choose the option that is best according to your organization’s security policies.
Note: The menus and options you see in your Microsoft 365 account may vary depending on several factors, including the level of service you have with Microsoft or if you purchased Microsoft 365 through a reseller. Reach out to your reseller or Microsoft support if you are unable to follow the directions here.
IN THIS ARTICLE
- Enable Automatic External Forwarding for All Mailboxes
- Enable Automatic External Forwarding for Individual Mailboxes
Enable Automatic External Forwarding for All Mailboxes
Log into your Office 365 Security & Compliance portal for Microsoft 365 and choose Threat management > Policy > Anti-spam or head directly to the Anti-spam settings page here: https://protection.office.com/antispamNote that the policies you see in your own admin may differ from those shown here, as these are only the default policies.
2Click on Anti-spam outbound policy (Default) and scroll to click the Edit protection settings link at the bottom of the sidebar.
3Find the section called Forwarding Rules, and the dropdown list called Automatic Forwarding Rules. Pull that list down and choose On – Forwarding is enabled. Click Save at the bottom. 
Enable Automatic External Forwarding for Individual Mailboxes
Log into your Office 365 Security & Compliance portal for Microsoft 365 and choose Threat management > Policy > Anti-spam or head directly to the Anti-spam settings page here: https://protection.office.com/antispamNote that the policies you see in your own admin may differ from those shown here, as these are only the default policies.
2Click + Create policy and choose Outbound.
3
Give your new outbound spam filter policy a Name and Description.
Click Next and search to find the user account you want to allow to forward, i.e. the email account that you are forwarding to Help Scout, which will display under the Users field after you select it.
Click Next again, scroll to the Forwarding rules section, and click the dropdown under Automatic forwarding rules. Choose On – Forwarding is enabled, then click Next.
Review the settings on the last screen and click Create to create your new outbound policy for the specified user(s).
Note: You may have other transport rules or spam policies in place at Microsoft 365 that block external forwarding in addition to the outbound spam filtering we’ve covered here. If automatic external forwarding is still blocked after adjusting these policies, you will want to reach out to your Microsoft 365 support for assistance in finding any further blocking that has been set up in your Microsoft 365 account.
Ref: https://docs.helpscout.com/article/1424-enable-external-forwarding-in-microsoft-365