solve wp email not sending issues

Very old wp site suddenly does not send emails, neither from contact forms nor from woocommerce cart. Disabled WP Mail Bank and set up FluentSMTP as alternative, but they both behave the same - when sending test email it fails because Invalid address: (From): contact@https://(mydomain)
I tried setting it up with outlook/Office365 API settings and while that all appears to be configured successfully it still doesn't work.