Headers are not formatted correctly in Outlook and Hotmail.

The header and unsubscribe-button is displayed correctly in gmail, but in outlook and hotmail, the header looks formated.
As far as i can tell, it is formatted using MIME.
This also happens when the URI doesnt contain non-Ascii symbols, and it isnt too long for the standard.
When both mailto and URI part is supplied, only the URI part is formatted.
Outlook is able to show headers correctly from other vendors, but doesnt support one-click-unsubscribe via URI, only Mailto.

Headers when inspected in outlook:

List-Unsubscribe-Post: List-Unsubscribe=One-Click

List-Unsubscribe: mailto:[email protected],

=?us-ascii?Q?=3Chttps=3A=2F=2Fexampleservice=2Eemsp-tst=2Eexample=2Edk=2Fapi=2Fv1=2FExternalEma?=

=?us-ascii?Q?ilAdministration=2Funsubscribe=2F83e598f1-4?=

=?us-ascii?Q?4be-411c-a4ca-e922de65a5a7=2F10=3E?=

Headers when inspected in gmail:

List-Unsubscribe-Post: List-Unsubscribe=One-Click

List-Unsubscribe: mailto:[email protected], https://exampleservice.emsp-tst.example.dk/api/v1/ExternalEmailAdministration/unsubscribe/83e598f1-44be-411c-a4ca-e922de65a5a7/10

Im using SendEmailAsync method in the SendGrid 9.24.3 nuget package