This article provides troubleshooting information for senders having trouble getting email delivered to Outlook.com users' inboxes.
Spam folder placement
Microsoft uses their proprietary SmartScreen® spam filter to help protect their users from spam. The SmartScreen® filter is influenced by a number of factors related to the sender, including the sending IP address, domain, authentication, list quality, complaint rates, content and engagement. SmartScreen® incorporates machine learning technology that helps the spam filter learn to recognize legitimate and spam email based on user interactions, so creating high engaging content is key.
Common causes of spam folder placement
- Poor sending reputation: Your sending reputation is a direct reflection of your commitment to following sending best practices. Microsoft is more likely to deliver your email to your subscribers' inboxes if they see a low rate of users marking your email as spam or phishing.
- One of the principal factors that affects your sending reputation and deliverability is your email complaint rate. Achieving and maintaining a low complaint rate can help you reach the inbox.
- To maintain your low complaint rates, sign up with Microsoft's Junk Mail Reporting Program (JMRP) and make sure all complainers are added to your suppression list.
- The JMRP is a free service that provides reports to senders on users that mark email as spam. New enrollees usually start to receive feedback in as little as 72 hours.
- Microsoft records a complaint when the subscriber clicks on the 'this is spam' button or if the subscriber moves the email directly to the junk folder. In both cases, an ARF notification message of the complaint is sent to you via the JMRP.
- Microsoft generally expects you to be able to audit your participation in the JMRP by checking your ARF messages. Queries to Microsoft asking them for audit information may or may not be returned. If there is some doubt about which IPs are included in JMRP, it may be faster just to reapply.
- In addition to complaints, Microsoft (Outlook.com) users have the option of marking emails as phishing. Microsoft's JMRP also returns reports about emails marked as phishing. Ensure that subscribers marking your email as phishing are added to your suppression list.
- To help prevent your messages being perceived as a phishing message, ensure that your email is easily recognized with clear branding in the friendly-from address and within the content. Always use valid, reputable URLs and domains in your headers and content. Do not link to known phishing websites.
- Authenticate your email using Domainkeys Identified Mail (DKIM), Sender Policy Framework (SPF) and Domain-based Message Authentication, Reporting and Conformance (DMARC).
- Sending from new IP addresses and domains: New IP addresses and domains do not have a sending history, so email sent from new IPs and domains often encounter deliverability issues. Over time as a sending reputation is built and you send engaging content with low complaint rates, deliverability improves.
- Ensure you warm up new IP addresses and domains over several weeks. Sending high volumes of email from a new IP address or domain will likely be perceived as spam and cause deliverability problems.
- Ensure all new IP addresses are added to the JMRP.
- Incorrectly configured DNS: A mis-configured DNS may cause problems connecting to Microsoft email servers or may cause Microsoft to perceive email from that server to be spam.
- Ensure all resource records such as A records and TXT records are properly configured for the domain.
- Ensure reverse DNS (PTR) records are properly configured for the IP address. Microsoft may not accept your email if the reverse DNS lookup fails.
- Try manually connecting to Microsoft's MX servers over port 25 from your sending system to ensure a connection is being made.
- Namespace mining: Trying to connect to Microsoft's servers in an attempt to verify email addresses without sending email may result in your email getting blocked. If you are not involved with namespace mining, check your servers to ensure they were not compromised by a hacker who is using them to attack Microsoft's servers.
- Not employing Email Authentication: Authenticating your email helps to prevent domain spoofing or fradulent use of your domain.
- Sender Policy Framework (SPF): Ensure your sending domain has an SPF record with all of your sending IP addresses.>
- Domainkeys Identified Mail (DKIM): Ensure there are no errors when signing your email messages with DKIM. Also, Microsoft sometimes makes slight modifications to content which can break DKIM. Ensure the c=tag in the DKIM signature is set to relaxed/relaxed. It allows for a little more tolerance for minor modifications to both the header and body of the message so the DKIM verification process is less likely to fail.
- Domain-based Message Authentication, Reporting and Conformance (DMARC): Microsoft may not accept email from senders who fail DMARC. Work towards publishing a DMARC record for your sending domain with a p=reject policy to help block unauthorized email using your domain.
- Excessive new Microsoft subscribers: Ensure that new Microsoft subscribers on any given send do not exceed 5% of the total Microsoft subscribers. So, if you are sending to 100,000 Microsoft subscribers for a single campaign, make sure that new Microsoft subscribers do not exceed 5,000. New subscribers are people that have recently opted-in to receive your email and have not received previous marketing email from you. Split up your campaigns if your new Microsoft subscribers exceed 5%.
In order to help senders troubleshoot sending problems, Microsoft returns SMTP error codes to senders for undelivered email. Gain access to your email log reports and look for these codes for every campaign encountering deliverability problems. Common error codes returned involve throttling and blocks due to poor sending reputation.
Error code examples from the Microsoft (Outlook.com) postmaster site
- 421 RP-001: The mail server IP connecting to Outlook.com server has exceeded the rate limit allowed. Reason for rate limitation is related to IP/domain reputation. If you are not an email/network admin please contact your Email/Internet Service Provider for help.
- 550 SC-001: Mail rejected by Outlook.com for policy reasons. Reasons for rejection may be related to content with spam-like characteristics or IP/domain reputation. If you are not an email/network admin please contact your Email/Internet Service Provider for help.
Microsoft Smart Network Data Services (SNDS)
Microsoft Smart Network Data Services (SNDS) is a program Microsoft offers to senders. SNDS provides data based on actual email sent to Outlook.com subscribers. The metrics include:
- Spam complaints
- SmartScreen filter results
- Spam trap hits
Microsoft troubleshooting tools and support
When troubleshooting blocks at Microsoft, you can open a support ticket directly with Microsoft to help determine a cause. Prior to opening a support ticket, do your best to troubleshoot and fix the cause and refrain from opening multiple tickets for the same issue or IP address. If you are being blocked, be sure to include a copy of the entire error message as it will help Microsoft troubleshoot the issue and may help towards a faster resolution.