> I have developed my signature so that nobody can replicate it fluently.
Robots that hold and move a pen have been created to forge signatures.
> I also use special one off archival ink that nobody else in the world has.
I’m not sure if you’re being serious or not because this is absolutely hilarious, but in the event that you are, does this have any purpose? You could use this excuse to secretly “poison” a contract that you intend on breaking (by using a normal pen to sign it).
> Emails do not have any default mechanism like that, especially if they only rest on servers of the interested parties.
Gmail accounts are free and support DKIM. If both parties conduct business over Gmail, those messages have irrevocable sender authenticity. This inability to refute the contents of an email spelled disaster in the USA for the Democratic political party during their 2016 presidential campaign.