What the receiver is telling you

Microsoft's warmup throttle. The IP has little or no sending history with Microsoft, so Exchange Online Protection defers most of what it sends until there is enough data to judge it. It is expected on any new dedicated IP and it lifts on its own as the IP builds a record. It is not a reputation problem yet; it becomes one if the early volume is high or generates complaints.

How to handle a soft bounce

Your server or sending tool retries soft failures automatically, usually for one to three days. Most clear on their own. The mistake is leaving an address that soft-bounces on every step in an active sequence: each attempt is logged, and a mailbox that has been full or unreachable for two weeks is not going to read a follow-up. Three consecutive soft failures is the point to remove it. Track soft bounces separately from hard ones; they are a different signal and receivers weight them differently.

What to do

1. Warm the IP deliberately: a few dozen messages a day to engaged Microsoft-hosted recipients, doubling every few days over two to four weeks.
2. Make sure reverse DNS, SPF, DKIM and DMARC are all in place before the first send.
3. Let retries handle the deferrals; do not resend manually.

don't Do not push volume to 'get through the warmup faster'. High volume from an unknown IP is what turns 4.7.850 into 5.7.708.

Decode the whole bounce

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

Common questions