Outlook
Outlook is an email provider for predominantly Outlook, Hotmail, and Live freemail addresses, as part of Microsoft. For legitimate messages going to the spam filter or getting blocked, you'll likely need to file a false-positive report with Outlook support. For globally-blocked IPs, the adminstrator of the IP will need to request delisting directly.
Domains
hotmail.com · outlook.com · msn.com · live.com
Codes
421 · 450 · 451 · 452 · 501 · 550 · 554
- 421↑
421 4.3.2 Service not available [outlook.com]
This indicates that the domain is not currently accepting email.
- 450↑
450 4.7.3 Organization queue quota exceeded. [outlook.com]
The receiving email domain is currently receiving an email at a high rate. This messages indicates the domain is not currently able to receive emial. Sending email in the future will most likely be successful.
- 451↑
- 451 4.3.2 Temporary server error. Please try again later ATTR17 [outlook.com]
451 4.4.0 Message failed to be replicated: No healthy secondary server available to accept replica at this time. [outlook.com]
The sender's domain is currently unable to accept this message. Sending email in the future will most likely be successful.
451 4.7.0 Temporary server error. Please try again later. PRX6 NextHop: outlook.com [outlook.com]
The sender's domain is currently unable to accept this message. Sending email in the future will most likely be successful.
451 4.7.650 The mail server [x.xx.xx.xx] has been temporarily rate limited due to IP reputation. For e-mail delivery information, see https://postmaster.live.com (S843)[#.prod.protection.outlook.com]
Outlook has determined that the sending IP address has a low reputation, so messages are now temporarily rejected. See Microsoft's documentation on how to determine the source of this poor reputation and how to improve deliverability.
451 4.7.651 The mail server [x.xx.xx.xx] has been temporarily rate limited due to IP reputation. For e-mail delivery information, see https://postmaster.live.com (S3114) [#.prod.outlook.com #]
Outlook has determined that the sending IP address has a low reputation, so messages are now temporarily rejected. See Microsoft's documentation on how to determine the source of this poor reputation and how to improve deliverability.
- 452↑
452 4.3.1 Insufficient system resources (TSTE) [outlook.com]
The receiving mail server is currently out of storage space. The administers at the receiving domain will need to resolve this issue. Once they've done this, they'll be able to start to receive messages again.
- 550↑
- 550 5.5.0 Requested action not taken: mailbox unavailable. [#.eop-nam12.prod.protection.outlook.com]
550 5.7.1 Service unavailable, MailFrom domain is listed in Spamhaus. To request removal from this list see https://www.spamhaus.org/query/lookup/ (S8002) [#.eop-nam02.prod.protection.outlook.com]
The MailFrom domain is also known as the Return-Path header domain, and is used to validate SPF authentication (it's not always the same domain as your From address for the message). Outlook checks your MailFrom domain against the public block list Spamhaus. Spamhaus is a very reputable block list with few false-positive listings. You must cooperate with Spamhaus volunteers to resolve the listing. Remember that even once the listing is removed, it may take receivers up to 24 hours to refresh their cache and to see delivery resume.
550 5.7.1 Unfortunately, messages from [x.xx.xx.xx] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [#.eop-nam02.prod.protection.outlook.com]
This is Microsoft's way of throttling your sending IP, possibly related to IP reputation classification. It should automatically expire on its own and is generally caused by sending too much traffic too fast.
550 5.4.1 All recipient addresses rejected : Access denied [#.eop-nam02.prod.protection.outlook.com]
This could be due to an active block on the sender for abuse reasons, but typically it's a policy that only specific senders/servers are allowed to send mail to this host. Reach out the recipient directly for options to add the sender to their 'allow list'.
- 554↑
554 5.2.122 The recipient has exceeded their limit for the number of messages they can receive per hour. For more information go to http://go.microsoft.com/fwlink/?LinkId=526653. (#) [outlook.com]
The Microsoft 365 or Office 365 recipient has exceeded the number of messages they can receive per hour from all senders.
554 5.2.121 The sender has exceeded the limit for the number of messages they can send to this recipient per hour. For more information go to http://go.microsoft.com/fwlink/?LinkId=526653. [#.prod.outlook.com #]
The sender has exceeded the maximum number of messages they're allowed to send per hour to a specific recipient in Exchange Online.