Microsoft weights sender reputation via SNDS and JMRP, and rejects unauthenticated bulk mail to consumer Outlook.com addresses.
What reverse DNS (PTR) records are#
A PTR record maps a sending IP address back to a hostname. Mailbox providers check that the PTR resolves and that the hostname's A record points back to the same IP (forward-confirmed reverse DNS).
Why it matters#
Gmail's sender guidelines require valid forward and reverse DNS. Missing or generic PTRs are a classic spam signal and cause outright rejections at many gateways.
Setting up reverse DNS (PTR) records for Outlook and Microsoft 365#
- Ask your hosting or ESP provider to set a PTR for each sending IP.
- Use a hostname under your domain (mail1.example.com) rather than the provider's generic name.
- Create the matching A record so forward and reverse agree.
- Use the same hostname in the SMTP HELO/EHLO banner.
How Outlook and Microsoft 365 reports results#
Open a delivered test message in Outlook and Microsoft 365 and view the original or headers. Look for Authentication-Results and any provider-specific verdict headers. Use the provider's sender dashboard for aggregate reputation.
Common mistakes#
- Generic PTRs like 203-0-113-10.provider.net.
- HELO names that do not match the PTR.
Frequently asked questions#
Can I set PTR records in my own DNS?
No. PTRs live in the IP owner's reverse zone. Your hosting provider or ESP sets them, though some offer self-service.
Does Outlook and Microsoft 365 require reverse DNS (PTR) records?
Microsoft weights sender reputation via SNDS and JMRP, and rejects unauthenticated bulk mail to consumer Outlook.com addresses. Treat reverse DNS (PTR) records as required for any meaningful volume.