Webmail/cPanel failing to open when using service subdomain - Over standard port expect “cpanel.” service subdomain, not “127.0.0.1”!

Symptoms

Accessing Webmail from Email Accounts feature in cPanel fails and the following error is logged in the cPanel error log. This behavior only occurs when using a service subdomain such as cpanel.domain.tld:

CONFIG_TEXT: [2026-06-11 16:48:41 +0300] die [Internal Death while parsing ./frontend/jupiter/mail/webmailform.html.tt 2485412] Template::Exception: [TYPE]=[undef] [INFO]=[Over standard port expect “cpanel.” service subdomain, not “127.0.0.1”! at /usr/local/cpanel/Cpanel/WebmailRedirect.pm line 272. ] [TEXT]=[] at cpanel.pl line 1134. cpanel::cpanel::cptt_exectag("/usr/local/cpanel/base/frontend/jupiter/mail/webmailform.html.tt", 1) called at cpanel.pl line 4656 cpanel::cpanel::run_standard_mode() called at cpanel.pl line 938 cpanel::cpanel::script("cpanel::cpanel", "./frontend/jupiter/mail/webmailform.html.tt") called at cpanel.pl line 331

Alternatively, when accessing cPanel or one of it's interfaces using a service subdomain, you may see that the request is redirected to 127.0.0.1 leading to a connection timeout.

Cause

There appears to be a conflict with internal proxying of localhost (127.0.0.1) with cpsrvd controlled interfaces. We have opened an internal case with our developers to review this behavior further. The case ID is CPANEL-53956 and any updates to this case will be posted to our change logs.

https://docs.cpanel.net/changelogs/ 

Resolution

Access cPanel without using the service subdomain, this can be done with either IP access, hostname access, or domain access with the 2083 port specified.

CONFIG_TEXT: domain.tld:2083
hostname:2083
domain.tld/cpanel