550 5.7.708 Access denied, traffic not accepted from this IP
Sample bounce line
550 5.7.708 Access denied, traffic not accepted from this IP.
What it means
Exchange Online is refusing mail from the sending IP. Microsoft's support article says it is generated when you send from an IP address with a low reputation, which more often affects new customers such as Microsoft 365 trial subscriptions. The NDR reference table (grouped with 5.7.705) says most of the tenant's traffic was detected as suspicious, so a ban was placed on the tenant's sending.
Why it happens
- Sending from an IP address with a low reputation, more likely for new customers, for example a Microsoft 365 trial subscription.
- Most of the traffic from the tenant is detected as suspicious, so the tenant's sending ability is banned.
How to fix it
- Only an email admin in the sending organization can fix this.
- During a trial subscription, contact Microsoft Support to request an IP address exception until Exchange Online licenses are assigned.
- Otherwise, make sure any compromises or open relays are resolved, then contact Microsoft support through your regular channel to have the block removed.
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