Plan requirement
| Subscription | Any plan |
| Access | Admin |
The bounce reads 550 5.7.520 Access denied, Your organization does not allow external forwarding. Please contact your administrator for further assistance. AS(7555). It is a Microsoft 365 tenant policy blocking external forwarding, not a Zendesk problem, and no setting on the Zendesk side will change it.
Why do I get access denied connecting Office 365?
- That 550 5.7.520 bounce, or an access denied message when saving a forwarding rule.
- The rule saves and mail is not forwarded.
- It worked for one mailbox and not another.
Resolution steps
1. Ask your Microsoft 365 administrator to allow the forwarding
Microsoft blocks automatic external forwarding by default as an anti-exfiltration measure, through the outbound spam protection on the tenant. Your administrator allows automatic external forwarding for your Zendesk support address, usually for specific mailboxes rather than for everyone.
This is the cause in most cases, and it needs somebody with tenant rights. There is nothing an agent or a Zendesk admin can do about it from this side.
2. Check you have rights on that mailbox
Setting forwarding on a shared mailbox needs permissions on the mailbox itself, which are separate from being able to read it. That is why it works for your own and not for the shared one.
3. Check for a retention or compliance policy
Some policies prevent forwarding entirely on the mailboxes in scope. Then forwarding is not the route at all, and step four is the answer rather than a workaround.
The alternative that avoids the policy
The Microsoft Exchange connector does not depend on a forwarding rule, so a tenant policy that blocks forwarding does not block it. It needs administrator consent once, and after that there is no forwarding rule to be denied.
For organisations with strict tenant policies that is usually the easier path, and it is worth proposing before a long conversation about exceptions.
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