Microsoft error 5.7.708 "traffic not accepted from this IP" — how to get unblocked

Short answer: Microsoft has (usually temporarily) blocked your sending IP at their edge. 5.7.708 ("Service unavailable. Access denied, traffic not accepted from this IP") is Exchange Online refusing the connection itself — your content never gets evaluated. It's IP-reputation-driven and common for cold-email infrastructure on shared or recently-acquired IPs.

Why it happens

• IP reputation at Microsoft specifically — their internal lists are independent of public blacklists; you can be clean on Spamhaus and still blocked here.
• Shared-pool contamination — on ESP shared IPs, someone else's Outlook complaints block the pool.
• Volume-pattern flags from young infrastructure — part of Microsoft's 2026 crackdown on cold-email patterns (ML-based, engagement-weighted).

Fix sequence

1. Confirm which IP is blocked — it's in the bounce; on shared pools, report it to your ESP (it's their problem to rotate or delist).
2. Dedicated IP? Use Microsoft's delist portal (sender.office.com): submit the IP, verify by email, typically processed within 24-48h. Free — never pay anyone for this.
3. Fix the underlying signals before resuming: authentication aligned (grade it), rDNS/FcrDNS proper, volume ramped gently, engagement earned.
4. Register with SNDS (Microsoft's sender portal) for complaint-rate visibility on your IPs — note their spam-trap data was removed in July 2026, so pair it with blacklist monitoring for early warning.

Does 5.7.708 expire on its own?

Sometimes — light blocks age out in days when the traffic pattern stops. But delisting + fixing the cause is faster and prevents the block-relist cycle that gets IPs permanently distrusted.