---
title: 554 5.1.0 The Sender's Address Was Not Allowed
description: This is the response our platform returns if you are trying to send a message using a domain or address that is not present on a server's Sending Domains Whitelist, or if the domain or address is spec
---
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# 554 5.1.0 The Sender's Address Was Not Allowed
This is the response our platform returns if you are trying to send a message using a domain or address that is not present on a server's [Sending Domains Whitelist](https://help.socketlabs.com/docs/sending-domains-whitelist?hsLang=en), or if the domain or address is specifically blocklisted from processing messages through a specific server.
### Sending Domains Whitelist
The Sending Domains Whitelist is a security feature for SocketLabs On-Demand customers. The Sending Domains Whitelist allows for a server to be restricted to only accept messages for delivery that utilize specific addresses or domains in the From field. Messages from addresses or domains that are not on your list will not be sent. This applies to automated messages as well.
Addresses and domains can be added or removed from the Sending Domains Whitelist in the On-Demand Control Panel. To edit the Sending Domains Whitelist for your server follow these steps:
1. Log-in to your [On-Demand account](https://cp.socketlabs.com/)
2. Select the "View" button next to the server for which you'd like to update the Sending Domains Whitelist
3. Using the top menu bar click on "Configuration"
4. Select "Sending Domains" from the Configuration drop-down menu.
> ### Domains are added by using the "@example.com" syntax.
Addresses and domains may be added by a SocketLabs administrator and these cannot be removed. Please see our article on the [Sending Domains Whitelist](https://help.socketlabs.com/docs/sending-domains-whitelist?hsLang=en) for more information.
SocketLabs Address Blocklist
The SocketLabs spam detection systems, or any SocketLabs administrator at the request of a customer or as a result of Acceptable Use Policy violations, may initiate a block against specific addresses or domains from processing mail through a given server. This action is usually taken in lieu of service interruption. Specific addresses or entire domains that are generating and sending spam, or messages in violation of our policies may be blocked. Initiation of any block will be addresses via a SocketLabs Compliance ticket, in which a customer has the ability to have the block removed by addressing the underlying concern about the associated messages.
### Common Causes of Address/Domain Blocklisting
1. Compromised address (i.e. weak Exchange user password)
2. Backscatter spam
3. Auto-Forward spam
4. Compromised web form
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