Thats why I validate the DKIM signatures before touching that header, meaning 
the DKIM signature is already validated and fine. Then I put my validation 
header, which the MUA then can “consume”, but also delete other validation 
headers so no malicious party can pre-fill the email with a valid validation 
header.

None is validating DKIM locally, and if someone do, it would be easy to write 
an exception for that user.

 

Also, another thing that borks the DKIM signatures is the 8BITMIME to 7BITMIME 
down-conversion which is required for my scripts inside mail server to work 
properly.

 

Also, another thing I do, is cut off subjects at 100 characters. Reason I do 
that, is that subjects over 100 characters tend to crash certain MUAs so I have 
to keep the subjects low to avoid certain MUAs from silently crashing.

 

Från: Hans-Martin Mosner via mailop <[email protected]> 
Skickat: den 15 januari 2024 08:56
Till: mailop <[email protected]>
Ämne: Re: [mailop] Samsung and SIZE

 

Am 15.01.24 um 07:54 schrieb Sebastian Nielsen via mailop:

 That header is supposed to be attached by the originating MUA, and I don't 
*think* transit MTAs are permitted to rewrite it...

Problem is, that when MUA or first MTA has a incorrect date set, the email 
comes like last in inbox... have seen emails set with 1970-01-01 00:00:00 Or, 
even worse, it has a date that is like, several months off, so you have to 
SEARCH your inbox after that unread email that was popped into the middle.
 
Thus to avoid that irritating problem, both for my users, and for myself, I 
just set the Date: header to the server time, correcting any incorrect dates.
 
Whats so wrong with it.

Mailers creating DKIM signatures are likely to include Date:, so your 
"correction" would invalidate many DKIM signatures. It's up to your users to 
decide which is less inconvenient, especially if you always modify the header 
instead of only when the date is off by more than a day or so.

Cheers,
Hans-Martin

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