The DNS record(s) used for e-mail service (usually the A mail record) should be cloud at DNS tab on Cloudflare dashboard for your domain and the MX record should point to a hostname that is set to that unproxied (usually the A mail ) with DNS only record, otherwise your e-mails will not work as it seems to be the case.
The A mail record should contain the value of an IP address of your hosting provider/email server.
the hostname (DNS record) used for e-mail send/receive should be cloud (usually it’s the A mail ), while the MX record should point to a hostname (usually the A mail ) that is set to
Kindly, consider reading the article from belove under the section “ Best practices for MX records on Cloudflare → Follow these guidelines to ensure successful delivery of your mail traffic: ”.
I would suggest looking into below articles how to propperly setup e-mail configuration to make sure it works while your domain is using Cloudflare and is being proxied ( cloud).