Fix Email Error 550 5.7.364 Reverse DNS and Spam Rejection in Outlook
Question details
The user needs to resolve an email delivery failure resulting in error code 550 5.7.364.
- Product
- Microsoft Outlook / Exchange Online
- Device & OS
- not provided
- Scenario
- Sending outbound emails to external recipients from an Exchange or Microsoft 365 account.
- Observed behavior
- Outgoing emails bounce back with a Non-Delivery Report (NDR) showing error 550 5.7.364, indicating the sending server has an invalid or missing PTR (Reverse DNS) record, or is failing spam evaluations.
Before troubleshooting, review the Non-Delivery Report (NDR) carefully to identify the exact sending IP address mentioned and verify if the bounce-back occurs with all external domains or just one specific recipient.
Configure a Valid Reverse DNS (PTR) Record
The most common cause for error 550 5.7.364 is a missing or improperly configured PTR record. You must coordinate with your mail hosting provider to set this up.
Recipient mail servers perform a reverse DNS lookup to verify that the IP address sending the email matches the domain name it claims to be from. If this check fails, the email is rejected to prevent spam.
Open the Non-Delivery Report (NDR) email you received. Look for the technical details section at the bottom to find the specific sending IP address that was rejected by the recipient server.
Reach out to the IT administrator, Internet Service Provider (ISP), or cloud hosting provider that manages your outbound IP address. Request them to configure a Reverse DNS (PTR) record for that specific IP.
Ensure that the new PTR record resolves directly to your mail server's fully qualified domain name (FQDN), and that the FQDN also has a standard 'A' record pointing back to the same IP address.
Verify SPF, DKIM, and DMARC Authentication
Recipient servers increasingly demand strict email authentication. Misconfigured SPF or DKIM records can contribute to a 550 5.7.364 rejection.
Check IP Blacklist Status and Email Content
If your IP address has been flagged for suspicious activity, or if the email content triggers spam filters, the receiving server will reject the message.
Ensure Uninterrupted Productivity with WPS Office
While resolving complex server-side email routing and DNS errors requires administrative access and propagation time, your daily document work shouldn't have to wait. WPS Office provides a fully featured, lightweight, and highly compatible alternative to Microsoft Office for all your offline and online document needs.
- 1. Download the software: Visit the official WPS Office website and click the free download button for your operating system.
- 2. Install WPS Office: Run the downloaded installer file and follow the quick on-screen instructions to complete the setup.
- 3. Start creating documents: Open WPS Office and instantly create, open, or edit your existing Microsoft Office files with full layout preservation.
Frequently Asked Questions
What exactly is a Reverse DNS (PTR) record?
A Reverse DNS or PTR (Pointer) record does the opposite of a standard 'A' record. Instead of linking a domain name to an IP address, it links an IP address back to a domain name. Mail servers use this to verify the identity of the server sending the email.
Can I fix error 550 5.7.364 as a standard email user?
No, standard users cannot resolve this error directly. Setting up PTR records and managing DNS or IP blacklists requires administrative access to the domain hosting panel or the internet service provider's network settings. You must forward the NDR to your IT administrator.
Why did this error suddenly appear when my email was working fine yesterday?
This can happen if your Internet Service Provider recently assigned your mail server a new IP address that lacks a PTR record, or if your existing IP address was suddenly added to a global blacklist due to a compromised account sending spam.
Is error 550 5.7.364 related to Microsoft 365 specifically?
While the specific error code '5.7.364' is frequently generated by Exchange Online and Microsoft 365 servers during spam evaluation, the underlying issues—missing PTR records, bad IP reputation, or failing SPF checks—are universal email standards enforced by most modern email providers.
