Internet-Security.com TCP port 26 details

TCP port 26 is commonly used as an alternate SMTP port by shared hosting providers to bypass ISP blocks on port 25.
cPanel/WHM servers using Exim often enable “Alternate SMTP Port 26” for outbound mail from clients.
Hosting companies such as HostGator and Bluehost have historically documented SMTP service on port 26 for their shared hosting customers.
Windows mail servers like SmarterMail and MailEnable can be configured to listen on TCP 26 for SMTP submission, and some providers deploy it this way.
hMailServer also supports adding TCP 26 as an additional SMTP port in environments where port 25 is filtered.
Because SMTP is sometimes exposed on port 26, attackers and spammers may scan it to find misconfigured open relays or to evade port-25 restrictions.
Outside these alternate-SMTP deployments, there is no mainstream, modern protocol widely associated with TCP 26.

TCP 26