Sender ID

Internet Security. A deprecated email authentication standard that checked that a domain authorized a given email address to send on its behalf. RFC 4406 defines this standard.

This standard fell out of favor for two reasons:

• It relies on a Purported Responsible Address (PRA) in the email header. RFC 4407 defined this standard. The PRA conflicted with existing email forwarding and mailing list mechanism and caused deliverability issues.
• Microsoft owned the patents for key parts of the standard. That was incompatible with many open source licenses.

To authenticate email, organizations moved on to domain authentication.

To learn more, see the Twilio Email Infrastructure Guide.