If you mean signed only messages, this is not supported and will not be supported, please see here about why not:
https://github.com/M66B/FairEmail/blob/master/FAQ.md#user-content-faq12
Not suggesting any change here, but just a sharing a thought, as I think authentication and privacy are very important topics - and of course FE is a strong advocate of same.
I'm kind of in agreement with the comments on signing as they apply to typical email communications; however there are certainly cases for which authentication holds some special importance, as the author of those articles points out.
E.g. the Linux kernel release emails from Greg Kroah-Hartman - these are signed and not encrypted. While the keys are on keyservers, of which I am not a fan, they are available to be checked [1]
Author asks if a signature was missing would you react? Actually yes - quite fervently in this case when it did happen, when Greg's protege did a stable kernel release without a valid signature for kernel.org or linuxfoundation.org.
There are other authentication scenarios which are not about email, at least today - signing a document for example. An instruction to buy or sell shares - often the banks processes require an email as well as a phone call to confirm - a signed email would actually work, but it is not a part of most if not all processes I am aware of (I know that industry very well). It may happen one day, but its not even close today. Even though the email clients that are used (typically Outlook) can show that the email has a valid signature from the client.
His primary argument, is that the ability to sign comes at a cost - programming complexity and risk associated with it. And for cases like those above, where authentication is important but privacy is not, signing may well make sense. In many, perhaps all, cases it also probably makes sense to use a desktop client rather than a phone to achieve this.
Thank you Marcel for creating the best damn email client bar none!!
[1]
https://www.kernel.org/category/signatures.html
