Unable to set up an email account hosted in Plesk in an email client when a domain is behind Cloudflare: The connection to the server failed

Symptoms

• A domain is behind Cloudflare proxy.

• When setting up an email account of this domain in a mail client (Outlook, Thunderbird, Mail for iOS, etc.), the operation fails due to a failed connection to the mail server.

  Examples of error messages:

  • Outlook:

    Log onto incoming mail server (IMAP): The connection to the server failed.

  • Thunderbird:

    Unable to log in at server. Probably wrong configuration, username or password.

  • Mail for iOS:

    The IMAP server "example.com" is not responding. Check your network connection and that you entered the correct information in the "Incoming Mail Server" field.

  • PHP script:

    Connection could not be established with host example.com

Cause

Cloudflare proxies only HTTP/HTTPS traffic and blocks other traffic including mail. A mail client tries to fetch the real IP address using a domain name to set up a connection, but fails because the request ends up on the Cloudflare side.

Resolution

For manual configuration

• Use mail.<domain_name>:

  1. Disable proxy traffic for mail.example.com in Cloudflare dashboard (if it is enabled).

  2. Set up an email account in a mail client using mail.example.com for incoming/outgoing mail server.

  Note: Issue a wildcard SSL certificate for the domain example.com to add an email account using a secure connection.

• Configure an email account using the server hostname (if it is not behind Cloudflare) for incoming/outgoing mail server.

  Note: Secure the mail server hostname with an SSL certificate to add an email account using a secure connection.

• Configure mail client using Plesk mail server IP address.

  Note: In this scenario, the customer will receive an SSL warning when trying to set up an email account.

For autodiscovery

Note: For this solution to work, disable proxy traffic for mail.example.com in Cloudflare dashboard (if it is enabled).