This security feature allows users to provide specific email addresses and/or domains that are permitted in the MAIL FROM SMTP protocol command issued during the mail relay process. Once a single domain or address is specified, all other domains and addresses not listed in the whitelist will be rejected at the SMTP protocol level.
This Feature also applies to automated messages, such as Out-Of-Office responders.
The following SMTP error is issued when an address does not match the whitelist:
554 5.1.0 The Sender’s Address Was Not Allowed
The Sending Domains Whitelist feature does NOT allow for the bypassing of the required SMTP authentication process. The Sending Domains Whitelist does not apply to messages injected via the HTTP Injection API.
SocketLabs Acceptable Usage Policy specifically requires that your mail must be sent from an address at a domain that is currently registered to you and under your control. For example, you may not use a from address including a domain from consumer email addresses such as Yahoo, Hotmail, AOL or Gmail, etc. or any other domain not under your full ownership and control.
Users in violation of this policy may have the Sending Domains Whitelist feature disabled to prevent further violations. Domains that are added with the “Required” status type can only be removed by SocketLabs Support team members.