These would be the first things I'd ask your web-host about:
(1) make sure you're running your website with a valid SSL certificate.
(2) use the secure SMTP option (usually by specifying the port number e.g. 587 instead of 25 (or similar)
Ask your host, or email provider or ISP (whoever provides the email server) how to configure the secure mail, and ask your web-host about installing SSL for your site.
For SSL, you could install Let's Encrypt, an SSL service available (I would assume) for most hosting companies e.g. in cPanel, Plesk etc. They might have other options e.g. to purchase third-party SSL services via some sort of subscription arrangement.
Hope that covers your question.