The dc-##### subdomain is added to overcome a conflict created when your SRV or MX record resolves to a domain configured to proxy to Cloudflare.
Do not orange-cloud DNS records used to receive mail: Cloudflare does not proxy mail traffic by default.
Seems like your A type mail DNS record is set either to cloud (proxied) and/or your MX type DNS record points to yourdomain.com (which is also proxied), while it shuld be rather pointed to an unproxied cloud (DNS-only) mail.yourdomain.com hostname.
Cloudflare’s default configuration only allows proxying of HTTP traffic and will break mail traffic.
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
I recommend to re-check things mentioned in below articles how to propperly setup e-mail configuration to make sure it works while your domain is using Cloudflare:
May I ask have you try sending and receiving your e-mails?
Furthermore, have you checked when using your e-mail client, if your e-mail client (MS Outlook, Mozilla Thunderbird, Apple Mail, etc.) have incomming/outgoing (POP3/IMAP/SMPT) server set to mail.yourdomain.com (and you have had smtp.yourdomain.com too somewhere above) instead of yourdomain.com?
Therefore, are you using secure (SSL) connection and good ports?