Too long URLs in the List-Unsubscribe header causes the DKIM signature verification to fail

[PlanetIrata]

When Nodemailer format the List-Unsubscribe header on more than one line, it may cause a DKIM signature verification failure. This is the case with my SMTP server. Note that I do NOT use the dkim parameters of Nodemailer, the DKIM signature is generated by my own SMTP server, and as soon as the List-Unsubscribe header is generated on two lines, the DKIM signature verification is reported as fail, but pass until the List-Unsubscribe is kept on one line. Tested on a Gmail recipient.

This works (one line List-Unsubscribe because the url is short):

Authentication-Results: mx.google.com;
       dkim=pass (...)
List-Unsubscribe: <http://example.com/campaign/unsubscribe?dummy=short>

This fails (two or more lines for the List-Unsubscribe because the url is longer):

Authentication-Results: mx.google.com;
       dkim=fail (...)
List-Unsubscribe:
 <http://example.com/campaign/unsubscribe?dummy=longer_url_with_several_params>

Workaround: I generate the List-Unsubscribe header myself with the headersprops of Nodemailer, it is generated on one line and the DKIM verification works again for any URL:

  headers: {
      "List-Unsubscribe-Post": "List-Unsubscribe=One-Click",
      "List-Unsubscribe": {
        prepared: true,
        value: '<http://example.com/campaign/unsubscribe?dummy=longer_url_with_several_params>',
      },
  },

Maybe that this header specific parameter List-Unsubscribe should not be prepared by Nodemailer