Unable to set up a mail account on an external mail client (e.g. Outlook) when the domain name is using Cloudflare proxy:
Connection could not be established with host example.com
Unable to connect to example.com:587
The webmail [email protected] works correctly.
Cloudflare does not proxy the mail traffic, it can only proxy traffic going over the HTTP/HTTPS ports in a specific range: https://support.cloudflare.com/hc/en-us/articles/200169156
Mail client tries to fetch the real Plesk IP address using a domain name to set up a connection but fails because the request ends up on the Cloudflare side and the wrong IP is obtained.
There are 3 solutions available:
In Cloudflare console, do not proxy traffic on mail.example.com and configure email on mail.example.com.
Configure mail client using a hostname that resolves directly to Plesk mail server IP address.
Note: The mail server on that hostname should be secured in order to avoid an SSL warning when trying to set up an email account.
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. There are no ways to avoid such warnings.