[MlMt] DKIM validation at client level

[Bill Cole]

On 5 Oct 2017, at 17:05, Alexandre Takacs wrote:

> Hello
>
> Sorry if I missed it, but I can't seem to find information on this 
> topic.
>
> Is there any provision in MM to validate DKIM informations in received 
> mail (either built in or via some bundle) ?

None that I'm aware of. This is unsurprising, since DKIM validation 
after final delivery and IMAP retrieval is potentially problematic. It 
might work, but it might not for no reason of any piece of the delivery 
and rtrieval chain being wrong.

> Any pointer appreciated.

If I were to do this, I would FIRST check for an 
"Authentication-Results" header added by my own trustworthy server, if 
my own trustworthy server added such headers. Were that header to be 
absent, I would install the 'opendkim' package (available in MacPorts 
and probably Homebrew) and rig up something to pipe messages into the 
opendkim-testmsg tool an check the result code.

The value of DKIM validation at any point is dubious, given that anyone 
can DKIM-sign their messages for the cost of a domain and some DNS and 
MTA config clues.