On 24/12/2025 05:35, Dan Raymond via Postfix-users wrote:
The sendmail command (ie. /usr/sbin/sendmail) normally extracts the
sender's display name
from the comment field of /etc/passwd. This is used to populate the
"From" header. However,
when the -f option is used the /etc/passwd file is not consulted and
the display name is
instead set to the account name of the current user. This is both
incorrect and confusing
to the recipient since the display name does not match the sender's
account name.
For example:
# whoami
john
# cat /etc/passwd | grep "john"
john:x:1000:1000:John Doe:/home/john:/bin/bash
# echo -e "Subject: test\n\nthis is a test\n" | sendmail [email protected]
# su root
# echo -e "Subject: test\n\nthis is a test\n" | sendmail -f john
[email protected]
The resulting emails will have the following "From" headers:
From: John Doe <[email protected]>
From: root <[email protected]>
This also impacts php scripts which use the mail() function to invoke
sendmail.
Hi Dan
While this will not address your underlying point, I don't think that
your observation is 100% correct in the part where you stated "when the
-f option is used the /etc/passwd file is not consulted and the display
name is instead set to the account name of the current user."
If you do
cat /etc/passwd | grep "root"
you might find that the "root" that is being used is coming from the
comment field of /etc/passwd
John
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