How do I contact Postmaster for Outlook or Hotmail?

Question

How do I contact Postmaster for Outlook or Hotmail?

Hu SNDS 15

I appreciate this is most likely the wrong place to be asking this question, but I've been trying to find the correct place to raise an issue for a while now.

I'm trying to diagnose an issue when SENDING TO Outlook and Hotmail emails. My sending IP is being "temporarily rate-limited".

I've tried accessing https://substrate.office.com/ip-domain-management-snds/postmaster/ but it is currently returning a 500 error response.
I've also tried using https://sendersupport.olc.protection.outlook.com/snds but it consistently says there are no issues with the IP.
I've raised issues with https://olcsupport.office.com/ but there's no space to say the issue keeps coming back or to start a discussion with anyone.

I'd really like to figure how I'm meant to get support on with this type of issue.

Hornblower409 15,835 Reputation points

2026-01-26T14:32:57.4833333+00:00

Have you tried the Office 365 Anti-Spam IP Delist Portal?
https://sender.office.com/

Microsoft's general recommendations will take some time to improve your reputation.

https://learn.microsoft.com/en-us/answers/questions/5449685/ip-address-temporarily-rate-restricted

https://learn.microsoft.com/en-us/defender-office-365/external-senders-mail-flow-troubleshooting
Hu SNDS 15 Reputation points

2026-01-27T11:56:01.44+00:00

Part of the problem with https://sender.office.com/ is that it needs to email the address with issues to prove ownership and that's currently a no-reply email.
I managed to work with SNDS sender support as that's based on the IP, so I could email one address set-up to receive emails to prove ownership of the IP easily. Maybe I'll try doing the same or try temporarily setting up allowing replies.
Either way, it's yet another separate tool that may or may not work.
Łukasz Zaremba 0 Reputation points

2026-02-27T15:26:24.7233333+00:00

Any way to get 500 error fixed?
Hornblower409 15,835 Reputation points

2026-02-27T15:31:55.9966667+00:00

@Łukasz Zaremba said

Any way to get 500 error fixed?

What specific URL are you trying to access?
Łukasz Zaremba 0 Reputation points

2026-02-27T15:36:30.0333333+00:00
Hornblower409 15,835 Reputation points

2026-02-27T18:01:54.5866667+00:00

@Łukasz Zaremba said

500 Error from https://substrate.office.com/ip-domain-management-snds/postmaster/

I can reach it with no problem. Sorry, but I don't know why you can't.

I'm fairly sure that this is still the right link as it's referenced in this other Microsoft SDNS article. Can you reach this one? https://sendersupport.olc.protection.outlook.com/snds/faq
Hornblower409 15,835 Reputation points

2026-02-27T18:12:27.4166667+00:00

Redirect link from the old Postmaster Site any better?
https://postmaster.outlook.com/
Łukasz Zaremba 0 Reputation points

2026-03-01T08:30:32.37+00:00

@Hornblower409

Unfortunately no :-( Tried from few data centers, different VPNs, different countries and all give:

< HTTP/2 500
< content-length: 0
< server: Microsoft-HTTPAPI/2.0

Thanks for your attempts to help!
Łukasz Zaremba 0 Reputation points

2026-03-03T07:30:11.3833333+00:00

@Hornblower409

I've been digging deeper and it apparently breaks on OIDC page.

Can I kindly ask, is your Postmaster account "special" in any way? Did you have to do something extra to login?
Hornblower409 15,835 Reputation points

2026-03-03T15:26:44.3266667+00:00

@Łukasz Zaremba said

is your Postmaster account "special" in any way?

I don't have a "Postmaster account". Don't even know what that is.

Did you have to do something extra to login?

Nope. No login of any kind. As far as I can see, it's a plain, publicly accessible web site.
Łukasz Zaremba 0 Reputation points

2026-03-03T15:44:44.6733333+00:00

@Hornblower409

Sorry for my initial comment and thank you for your help. There appears to be some issues at MS side (from other forums I have read) and I think this is just wait and see for this moment, and let the folk there do their jobs.

All the best!
kathy warner 0 Reputation points

2026-03-04T13:34:23.9333333+00:00

I have hotmail.co.uk. I am receiving messages but I can't reply anymore. Does anyone know how to fox this not just on my phone but tablet as well from a very stressed OAP
Hornblower409 15,835 Reputation points

2026-03-04T17:41:55.63+00:00

@kathy warner said

I am receiving messages but I can't reply anymore. Does anyone know how to [fix] this

You need to use the "Ask a question" button at the top of this page and create a new Question. This provides much higher visibility to your issue than commenting on this post witch is only seen by people who are already following this question.

1 answer

Your answer

Hornblower409 15,835 Reputation points

2026-01-26T14:32:57.4833333+00:00

Have you tried the Office 365 Anti-Spam IP Delist Portal?
https://sender.office.com/

Microsoft's general recommendations will take some time to improve your reputation.

https://learn.microsoft.com/en-us/answers/questions/5449685/ip-address-temporarily-rate-restricted

https://learn.microsoft.com/en-us/defender-office-365/external-senders-mail-flow-troubleshooting
Hu SNDS 15 Reputation points

2026-01-27T11:56:01.44+00:00

Part of the problem with https://sender.office.com/ is that it needs to email the address with issues to prove ownership and that's currently a no-reply email.
I managed to work with SNDS sender support as that's based on the IP, so I could email one address set-up to receive emails to prove ownership of the IP easily. Maybe I'll try doing the same or try temporarily setting up allowing replies.
Either way, it's yet another separate tool that may or may not work.
Łukasz Zaremba 0 Reputation points

2026-02-27T15:26:24.7233333+00:00

Any way to get 500 error fixed?
Hornblower409 15,835 Reputation points

2026-02-27T15:31:55.9966667+00:00

@Łukasz Zaremba said

Any way to get 500 error fixed?

What specific URL are you trying to access?
Łukasz Zaremba 0 Reputation points

2026-02-27T15:36:30.0333333+00:00
Hornblower409 15,835 Reputation points

2026-02-27T18:01:54.5866667+00:00

@Łukasz Zaremba said

500 Error from https://substrate.office.com/ip-domain-management-snds/postmaster/

I can reach it with no problem. Sorry, but I don't know why you can't.

I'm fairly sure that this is still the right link as it's referenced in this other Microsoft SDNS article. Can you reach this one? https://sendersupport.olc.protection.outlook.com/snds/faq
Hornblower409 15,835 Reputation points

2026-02-27T18:12:27.4166667+00:00

Redirect link from the old Postmaster Site any better?
https://postmaster.outlook.com/
Łukasz Zaremba 0 Reputation points

2026-03-01T08:30:32.37+00:00

@Hornblower409

Unfortunately no :-( Tried from few data centers, different VPNs, different countries and all give:

< HTTP/2 500
< content-length: 0
< server: Microsoft-HTTPAPI/2.0

Thanks for your attempts to help!
Łukasz Zaremba 0 Reputation points

2026-03-03T07:30:11.3833333+00:00

@Hornblower409

I've been digging deeper and it apparently breaks on OIDC page.

Can I kindly ask, is your Postmaster account "special" in any way? Did you have to do something extra to login?
Hornblower409 15,835 Reputation points

2026-03-03T15:26:44.3266667+00:00

@Łukasz Zaremba said

is your Postmaster account "special" in any way?

I don't have a "Postmaster account". Don't even know what that is.

Did you have to do something extra to login?

Nope. No login of any kind. As far as I can see, it's a plain, publicly accessible web site.
Łukasz Zaremba 0 Reputation points

2026-03-03T15:44:44.6733333+00:00

@Hornblower409

Sorry for my initial comment and thank you for your help. There appears to be some issues at MS side (from other forums I have read) and I think this is just wait and see for this moment, and let the folk there do their jobs.

All the best!
kathy warner 0 Reputation points

2026-03-04T13:34:23.9333333+00:00

I have hotmail.co.uk. I am receiving messages but I can't reply anymore. Does anyone know how to fox this not just on my phone but tablet as well from a very stressed OAP
Hornblower409 15,835 Reputation points

2026-03-04T17:41:55.63+00:00

@kathy warner said

I am receiving messages but I can't reply anymore. Does anyone know how to [fix] this

You need to use the "Ask a question" button at the top of this page and create a new Question. This provides much higher visibility to your issue than commenting on this post witch is only seen by people who are already following this question.

Answer 1

To contact support for issues related to sending emails to Outlook or Hotmail, you can follow these steps:

Use the Delist Portal: If your sending IP is being temporarily rate-limited, you can request removal from the Microsoft 365 blocked senders list using the delist portal. This portal allows you to submit a request if you encounter errors when sending messages to Microsoft 365 recipients.
Follow Non-Delivery Reports (NDR): If you receive a non-delivery report (NDR), follow any instructions provided in the message. This may include contacting Microsoft support directly.
Contact Microsoft Support: Since external senders typically cannot open support tickets directly, you may need to ask the Microsoft 365 recipient to contact Microsoft Support on your behalf. They can open a support ticket related to your sending issues.
Check Common Problems: Review the common problems that external senders encounter in the article on troubleshooting email sent to Microsoft 365. This may provide insights into the specific issue you are facing.

If you continue to experience difficulties, it may be beneficial to ensure that your DNS settings are correct and that your sending reputation is being managed appropriately.

References: