SMTP (the protocol used to send email) is completely unsecure.  It’s been unsecure since it was created.

You know how you can put absolutely any return address on an envelope?  The same is true of SMTP.  You can put any address there at all and then it looks like it’s coming from my domain.  I’ve retired martin@martincwiner.com because of stupid spammers that ruin everything for everyone.

I’ve replaced it with a less efficient contact form on the ‘About’ page.