In this post, let’s have a look at the error message “5.7.513 – Service unavailable, Client host [$ConnectingIP] blocked by $recipientDomain using Customer Block list (AS16012607)” that you get when working with Microsoft 365 Exchange Online.
These are the errors that you usually receive when there is a problem in delivering the email message that was sent by you. These errors are generated and sent by Office 365. This is usually alled as DSN which stands for delivery status notification or in simple words bounce messages.
NDR or Non-delivery report is one of the common type of message that you receive which indicates to the user that the email was not delivered.
5.7.513 – Service unavailable, Client host [$ConnectingIP] blocked by $recipientDomain using Customer Block list (AS16012607)
The recipient domain has added your sending IP address to its custom blocklist.
The domain that received the email has blocked your sender’s IP address. If you think your IP address has been added to the recipient domain’s custom blocklist in error, you need to contact them directly and ask them to remove it from the blocklist.