[Mimedefang] Mailing list breaks DKIM?

Bill Cole mdlist-20140424 at billmail.scconsult.com
Fri May 28 14:02:49 EDT 2021

On 2021-05-28 at 13:14:16 UTC-0400 (Fri, 28 May 2021 10:14:16 -0700)
Kenneth Porter via MIMEDefang <mimedefang at lists.mimedefang.org>
is rumored to have said:

> On 5/28/2021 8:15 AM, Benny Pedersen via MIMEDefang wrote:
>> another maillist that breaks dkim :/
>> would it not be simple to not do this ?
> Does it? My server says the signature on your message is valid.

Yes and yes...

The list server adds the topic tag '[Mimedefang]' to the Subject header 
if it is missing it, replaces the From header with its own address in a 
"via" form (See the 2nd line of my attribution above), adds a footer, 
and may even re-encode the body in some rare cases. All of these break 
any normal pre-existing DKIM signature. Except for the From munging, all 
of these are common mailing list practices which have been in use since 
before the ancestors of DKIM were invented. DKIM is designed to break 
with traditional mailing lists. This is not in any way an accident of 
well-meaning naifs.

The list server ALSO routes its outbound messages through a MTA that 
recognizes the list server as a vouched-for entity and which therefore 
constructs its own DKIM signature for each message which aligns with the 
modified message's From header.

Bill Cole
bill at scconsult.com or billcole at apache.org
(AKA @grumpybozo and many *@billmail.scconsult.com addresses)
Not Currently Available For Hire

More information about the MIMEDefang mailing list