Viewing File: /usr/local/cpanel/etc/exim/acls/ACL_TEMPORARY_DOMAINS_OUT_BLOCK/disable_sending_from_temp_domains

# Don't allow sending mail from temporary domains

deny
    condition = ${if eq{${perl{is_temp_domain}{$sender_address_domain}}}{1}{true}{false}}
    message = "cPanel does not allow outgoing mail from temporary domains."