“550 5.7.708 traffic not accepted from this IP” — Microsoft bars the range

The difference from 5.7.606

Both codes come from Microsoft and look similar, but they mean different things:

• 550 5.7.606 — your IP is on the block list because something notable came from it. There is a self-service delisting portal for that, and it generally works.
• 550 5.7.708 — no mail is accepted from this range at all. The decision is not about you alone but about the network your address sits in. The portal here often replies that the address is not blocked — which is true and still no help.

The 450 4.7.708 variant is temporary: the mail stays queued and the attempt is repeated. It shows up on sudden volume jumps from a previously quiet address and often clears on its own if the volume stays even.

Why whole ranges are affected

Address ranges belonging to cheap server providers are used to a considerable degree for short-lived bulk projects. For a large receiver the range as a whole is therefore a poor risk, regardless of who happens to be renting a single address out of it. A freshly assigned address with no sending history carries especially little weight in that calculation.

This is unsatisfying, but it is the reality that flawless technical setup alone does not overcome.

What you can check and do

1. Secure the fundamentals. A PTR record pointing to a name that resolves forward to the same IP; a HELO name identical to that name; SPF, DKIM and DMARC complete. Without that base any request is refused — with it, it at least has a chance.
2. Verify it really is only Microsoft. If mail gets through to other receivers and fails only at Outlook, Hotmail and Microsoft 365 domains, that confirms the reading as a provider-specific range block.
3. Check the neighbours. If nearby addresses in the same range appear on several lists, you sit in a burdened network. That is the strongest indication that moving achieves more than any request.
4. Send through a relay. The most practical route for small senders: delivering through an established sending service uses their addresses and their history. Your own server keeps handling everything else.
5. File a request. Microsoft runs a dedicated sender form for this case. Realistically, clearance comes only with clean setup, a comprehensible sending purpose and no bulk marketing from the same address.

What achieves nothing

Repeated sending makes things worse, because rejected attempts feed into the same assessment. Filing the portal request several times does not help either — under 5.7.708 the address is not listed there at all; the portal is simply not the right tool.