Increase Outlook Deliverability


To improve deliverability in Outlook, it's crucial to gradually warm up new IPs, address FBL complaints from subscribers, maintain updated lists to avoid hard bounces, avoid spam trap addresses, configure sending infrastructure and content correctly, and maintain frequency and consistency in sending to avoid being labeled as a spammer.

For most email senders, especially those with a substantial base of subscribed customers, Microsoft Outlook's mailbox is one of their primary destinations. It's also known to be somewhat challenging to penetrate. Here's the information senders need to achieve the best deliverability for Hotmail and Outlook and ensure their messages end up in the inbox.

Whether marketed as Hotmail, Windows Live, MSN, or, Microsoft's Outlook service employs a set of criteria to decide which messages are deemed spam and which are not. Microsoft utilizes proprietary methods, like any other internet service provider. However, we know that to provide a "reliability" score, it examines signals such as content, authentication, and domain and IP reputation. If your score is below normal, your communications may be "delayed" or "filtered as spam."

Main Techniques for Outlook/Hotmail Deliverability

The following six recommendations will assist you in optimizing Microsoft Outlook deliverability:

1. Warm Up New IPs: Microsoft allows only 10,000 messages from new IP addresses per day. The rest of the communications sent from new IPs will be delayed. Delays are common in the process of building an IP reputation. Over a trial period of two to four weeks, delays will diminish and then cease as your reputation grows. The number of messages Microsoft successfully delivers on your first attempt will increase as your reputation grows.

Best Practices: To avoid delays, start with 2,000 traffic to Outlook/Hotmail, double each day until you see "RP-001 (DYNAMIC CODE) Unfortunately, some messages from a.b.c.d were not sent. Please try again. We have limits on the number of messages that can be sent per hour and per day. You can also check" and then slow down traffic until these delays are interrupted. Note: We strongly recommend senders use their own "custom bounce domain," "tracking domain," and "dkim sign" with their own domain.

2. Pay Attention to and Address FBL Complaints: Whether a subscriber uses the unsubscribe link or the spam button, it's essential to address their unsubscribe requests. Maintaining correspondence with unsubscribed subscribers will harm your reputation with Microsoft. To reduce this risk, SparkPost sends and manages Feedback Loop (FBL) complaints on your behalf.

Ideal Procedures: Include a message reminding subscribers where they opted to receive it. Ensure your messages are relevant to the subscriber and arrive with the expected frequency. Subscribers who do not engage with your messages should be unsubscribed. If 0.5% of subscribers complain, your sending capacity will be affected.

3. Reduce Hard Bounces of "Unknown User": Do you maintain good list hygiene? Are you sending to an outdated list with many inactive addresses? Microsoft interprets this as evidence of spamming or email collection.

Best Techniques: Keep your list updated for hygiene. Change the frequency to addresses that are between three and six months old and get rid of addresses that haven't been used in a year. Make a consistent effort to re-engage subscribers using various strategies. Unknown user rates typically range between two and three percent.

4. Avoid Spam Trap Addresses: These are addresses that ISPs and security forces use to find people who collect or send email spam.

Best Practices: Use soft and hard bounces to maintain list hygiene. Bounce notices can provide important details about how Outlook, or any other service, manages your emails. Keeping spam trap rates below 0.01% is crucial if you want to avoid reputation issues.

5. Correctly Configure Sending Infrastructure and Content: Microsoft considers proper configuration of infrastructure and content alignment as signs of a quality sender. Additionally, Microsoft uses SmartScreen, a proprietary content filter. To identify what constitutes good and unwanted mail, SmartScreen collects information from Microsoft's customers, as well as data on known phishing risks. Probability-based algorithms are used in filtering to differentiate between spam and valid email.

Best Practices: Make sure to use only reliable and legitimate URLs. Avoid using IP addresses in URLs. Publish your Sender Policy Framework (SPF) documents. Pay attention to HTML components, URLs, and content.

6. Frequency and Consistency in Sending: It's best to send from the same IP address or addresses, with the same volumes and frequencies, every month. Spammers typically "pop up" and then disappear from an IP. Senders who are infrequent but send in bulk once a month or every quarter can be a sign of a compromised server or a spammer.

Best Techniques: Maintain consistency. Segment the emails you send. Sending relevant material to a select group of interested subscribers should take priority over sending generic material to your entire list. To ensure readers quickly notice your call to action when scanning your message, place it at the beginning of your article. Keep links relevant to the content and avoid link shorteners like Tailor your material to your subscribers' interests. Instead of sending the same material to all users on your list, use dynamic content to segment and personalize.


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