Thunderbird+HTML Causing DKIM to fail

[fxnick101]

Im a Longtime thunderbird user.
I have spent hours narrowing this down to a thunderbird problem
Long story short:
We get emails from a contact form on our website, I reply to them.
The emails contain html. Using thunderbird to reply will cause the dkim to fail according to google:

dkim=neutral (body hash did not verify)

They also fail DKIM at mail-tester.com and dkimvalidator.com
Searching this forum, this error seems to get blamed on the mail server.
But, I have tried 2 other mail clients, Apple mail on OSX and mymail on IOS
Same server, same email message and it passes DKIM with both clients
Now the interesting thing:
Thunderbird will send the message in the 7 bit format:

Code: Select all

Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit

Apple mail uses:

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Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain;
	charset=us-ascii

myMail uses:

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Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: base64

In the research I have done this DKIM problem seems to have something to do the content encoding being the 7-bit.
And also that thunderbird chooses this encoding based on what the smtp server says it accepts.
Now if I send a pain text message using thunderbird, the email will pass DKIM
So I am pretty sure having html in the message causes this, I have not narrowed it down to what specific html in the message causes this.
Does anybody have any guidance on this?
I dont want to stop using thunderbird, there must be a work around..that I have not figured out.
Also: Im On the TB beta channel so using 88.0B2 at the moment

[tanstaafl]

I sent a email message to a address provided by dkimvalidator.com using version 88.0b2 under Windows 10 using my Fastmail IMAP account. Everything (DKIM and SPF) passed. It used:

Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit

Have you tried using a different account to see if its a email provider specific problem? Gmail would be a good choice (to test with).

Are you sending a encrypted or digitally signed message (OpenPGP)?

If the above doesn't help I suggest you retest using version 78.9.1 (latest production release). You could use custom setup to install it in a different directory. If that works okay then I suggest you try 88.0b1. You will have much better chances of somebody paying attention to a bug report if you can identify what version the bug was introduced in, and be able to reproduce the bug using a popular free email provider. If you do submit a bug report please post a link to it.

https://bugzilla.mozilla.org/home