Outlook Postmaster(y) page

To help the sender community, we are glad to share our experiences collected over the years with some ISPs. This page concerns Outlook.com, whose webmail is one of the most widely used in the world. Postmastery is fully integrated with the outlook postmaster JMRP (Junk Mail Reporting Program) and SNDS (Smart Network Data Service) services through its monitoring tools.

We will highlight below topics:

Outlook postmaster

Market share and history of MBP

Founded in 1996 by Sabeer Bhatia and Jack Smith as Hotmail, it was acquired by Microsoft in 1997 for an estimated $400 million and relaunched as MSN Hotmail, later rebranded to Windows Live Hotmail as part of the Windows Live suite of products. Microsoft phased out Hotmail in October 2011, relaunching the service as Outlook.com in 2012.

Although Outlook.com has lost market share to gmail.com, to this day it remains the second largest webmail by number of users in the world.

Anti-Spam Measures

To protect its messaging infrastructure, Outlook.com mostly relies on proprietary filters (SmartScreen), third-party filters (such as Symantec's Brightmail) and RBLs (such as Spamhaus).

Feedback Loop

Microsoft offers a free service called Smart Network Data Services (SNDS). Senders use SNDS to gain an understanding of important data about their reputation and email deliverability to Microsoft mailboxes.

SNDS provides a summary of IP addresses, including statistics like estimated inbox rate, complaint rate, and trap hits.

Within your SNDS account you have the option to subscribe to the Junk Mail Reporting Program (JMRP) - Outlook.com's free ARF complaint feedback loop.
Once configured, you will be able to retrieve the email addresses that have marked your email as spam in Outlook's webmail.

Outlook postmaster Technical & SMTP Tweaks

Forward-confirmed reverse DNS (FCrDNS) : IPs should have both forward (name-to-address) and reverse (address-to-name) Domain Name System (DNS) entries that match each other.

Authentication : Outlook.com validates inbound mail using SPF and DKIM.
Additionally, Microsoft recently announced that outlook.com will now honor the DMARC record of "p=reject" by rejecting the message if the domain fails DMARC.

List-unsubscribe header : Outlook.com supports the list-unsubscribe mechanism but only when a mailto:link is present. When a user clicks on the 'unsubscribe' option in the webmail, Outlook.com tries to read the mailto:link in the List-Unsubscribe header. If the mailto:link is missing, it moves all the messages to the Junk folder. All further emails from the same sender will be pre-routed to the Junk folder without notifying the sender through a JMRP complaint.

Steady per IP volume : Hotmail is very sensitive to sudden increases in volume coming from a specific IP.

Common Error SMTP Messages

421 4.4.1 Connection timed out. Total session duration: 00:10:01.6820500

450 4.7.3 Organization queue quota exceeded.
451 4.7.500 Server busy. Please try again later from [X.X.X.X]. (AS760) [BY2NAM05FT044.eop-nam05.prod.protection.outlook.com]
451 4.7.500 Server busy. Please try again later from [X.X.X.X]. (AS761)
451 4.7.500 Server busy. Please try again later from [X.X.X.X]. (AS843)
451 4.7.500 Server busy. Please try again later from [X.X.X.X]. (AS3110)
451 4.7.500 Server busy. Please try again later from [X.X.X.X]. (AS3113)
451 4.7.500 Server busy. Please try again later from [X.X.X.X]. (AS3115)
451 4.7.500 Server busy. Please try again later from [X.X.X.X]. (AS3116)
451 4.7.500 Server busy. Please try again later from [X.X.X.X]. (AS77712342) [SN1NAM04FT008.eop-NAM04.prod.protection.outlook.com]
451 4.7.650 The mail server [X.X.X.X] has been temporarily rate limited due to IP reputation. For e-mail delivery information, see https://postmaster.live.com (S775)
451 4.7.650 The mail server [X.X.X.X] has been temporarily rate limited due to IP reputation. For e-mail delivery information, see https://postmaster.live.com (S843) [HE1EUR01FT028.eop-EUR01.prod.protection.outlook.com]
451 4.7.651 The mail server [X.X.X.X] has been temporarily rate limited due to IP reputation. For e-mail delivery information, see https://postmaster.live.com (S844) [BY2NAM05FT004.eop-nam05.prod.protection.outlook.com]
451 4.7.652 The mail server [X.X.X.X] has exceeded the maximum number of connections. (S3115) [DB5EUR01FT051.eop-EUR01.prod.protection.outlook.com]
Andy mentioned this error is applied per IP range(not individual). Microsoft support wasn't even aware of this rule,haha. When this error occurs, it's good to open a ticket with Microsoft and request that they increase the max connection limit.
452 4.3.1 Insufficient system resources
452 4.5.3 Recipients belong to multiple regions ATTR38 [CO1NAM03FT062.eop-NAM03.prod.protection.outlook.com]

​​550 5.5.0 Requested action not taken: mailbox unavailable.
550 5.7.1 Unfortunately, messages from [X.X.X.X] weren't sent. Please contact your Internet service provider since part of their network is on our block list (AS3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [VE1EUR02FT058.eop-EUR02.prod.protection.outlook.com
550 5.7.1 Unfortunately, messages from [X.X.X.X] weren't sent. Please contact your Internet service provider since part of their network is on our block list (AS3150).

Do you have a specific error message you need help with? The Postmastery team is ready to assist, please share some details here.

Abuse Desk & Tech Support

To address issues with emails that are being sent to spam or are missing/blocked, you can initiate a support ticket by using the link https://olcsupport.office.com/. An automated reply is typically received, and further replies to these auto-responses may be necessary until the issue is resolved. The process is designed in such a way that multiple auto-replies are received before a human representative, who can provide assistance, is reached.

More information
If you want more information about this topic, please send us a message via our contact form.
We are always happy to assist!

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