To clarify this and this explanation for Sender:
:
In brief, From: in the message indicates the mailbox of whoever wrote the message, Sender: indicates the entity which sent a message on behalf of someone else, and To: and Cc: indicate the intended recipient mailbox. The RFCs define other header fields you may be interested in, as well.
I notice that alpine
inserts the senders FQDN as <user>@<domain>
in the Sender:
field. While the From:
field can be modified in alpine
by modifying the Customized-Headers
setting, attempts to set the Sender:
field fail.
This looks to be an anti-spam technique? How does, or does it, relate to Sender Policy Framework?
See also:
https://en.wikipedia.org/wiki/Email_authentication
https://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol#Related_Requests_For_Comments
https://en.wikipedia.org/wiki/Anti-spam_techniques#Strict_enforcement_of_RFC_standards