1) UK law is similar to the law in most commonwealth countries.
For a contract via email to be legally binding under UK law there needs to be:
An offer;
Acceptance of the offer;
Consideration (i.e., some form of payment);
An intention to be legally bound by the contract; and
Certainty as to what the parties have agreed.

https://businessadvice.co.uk/business-development/business-planning/are-emails-legally-binding/

Under USA law
https://www.icaew.com/archive/library/subject-gateways/law/legal-alert/2018-02/case-law-court-confirms-emails-can-create-legally-binding-contracts

2) Yes - they are a written form of communication.

3) Your reputation - by your own conduct - was already absolutely rubbish.  I cannot imagine how this could ruin it even more. What this claim proved was that you go to extreme lows to deceive people from their funds. The only person that has a fantasy that you have a "good reputation" - is you.

4) By making the claim that it is a donation and by falsely claiming that "there is no contract"  you make it absolutely obvious with your current argument  to everyone that:

If we were to accept your argument then using your own logic and terminology:

a) You made a written statement that you had no intention of keeping in an effort to get a non refundable "donation".
b) You used your "reputation" to convince him to accept that "promise".
c) You have now clearly and publicly stated that you had no intention of keeping that promise because you consider it a "donation".