Microsoft (Outlook.com and Microsoft 365) · permanent error
5.7.513: sending IP on the recipient's custom block list
The recipient domain added your sending IP address to its own custom block list, so its Microsoft 365 tenant refuses your mail.
- Microsoft
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.7.513
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The recipient's side. Their mail admin has to change something; you can tell them.
- What the server says
5.7.513 Service unavailable, Client host [$ConnectingIP] blocked by $recipientDomain using Customer Block list…
What it means
With 5.7.513 the block comes from the recipient domain, which has put your sending IP on a custom block list of its own. The bounce names the recipient domain and carries the reference AS16012607. Microsoft's guidance is to contact the recipient directly if you believe the listing is a mistake and ask them to remove your IP, since the list belongs to them.
Common causes
- The recipient's admin added your IP to their block list, often after receiving unwanted mail from it.
- You send from a shared IP that the recipient blocked because of another sender.
How to fix it
- 01Contact the recipient through another channel and ask them to remove your IP from their block list.
- 02Give them the IP address and the exact bounce text.
- 03If the IP is shared, ask your email provider whether you can move to another one.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Email nondelivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com
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