What the receiver is telling you

A reputation refusal on the connecting IP, one step short of an outright ban. Microsoft's filter has scored the IP poorly — often a new IP with no history sending volume, a shared range with mixed neighbours, or an IP that recently sent a burst of mail Microsoft's users disliked. It tends to appear on new dedicated IPs that were never warmed, and it usually clears with delisting plus a gentle ramp.

Why a policy block must not be treated as a bad address

Sending tools file every 5xx under "bounced", and the natural reflex is to scrub the address. For a policy block that is exactly wrong. The recipient exists and would have received the mail; the receiver refused it because of your domain, IP, authentication or content. Scrubbing throws away a lead and leaves the cause in place, so the next send produces the same block against the next thousand addresses. The right response is to stop sending from the affected domain, find what the receiver named, fix it, and resume at low volume.

What to do

1. Request delisting at sender.office.com.
2. Once cleared, warm the IP: a few dozen messages a day to engaged Microsoft-hosted recipients, doubling weekly.
3. Make sure the IP has forward-confirmed reverse DNS and that SPF, DKIM and DMARC are set on every domain sending through it.

don't Do not respond to a 5.7.708 by sending more from the same IP to 'establish reputation'. Volume without history is the trigger.

Decode the whole bounce

Paste the complete failure notice — every code and the receiver's wording — and get each part explained together.

Common questions