Yes, if your ISP blocks port 25 you can use any of our alternative SMTP ports to send authenticated mail through our servers. Start with port 465 (SSL required) or port 587 (TLS supported). These ports are specifically provided so you are not forced to use your ISP's lower-quality SMTP relays. We maintain a broad list including 23, 26, 2025, 2525, 6025, 6465, and 8080 to ensure connectivity even as ISPs expand their blocking policies.

Many ISPs block port 25 and many others are starting to block other alternate SMTP ports as this is the standard port for mail delivery. They block the port for a variety of reasons; the most common reasons are to prevent you from running your own mail server and to stop devices on their network that are infected with spyware or malware from sending and spreading spam. Port 25 is not available on our primary mail systems to prevent incoming spam from going around our gateways. The variety of ports we offer directly addresses these restrictions so your applications and scripts can deliver mail without interruption.

#Why ISPs and Mail Systems Restrict Port 25

Port 25 is the traditional port used for SMTP communication between mail servers. Consumer ISPs block outbound traffic on this port to reduce spam originating from their networks. Malware-infected machines and unauthorized mail servers are the primary targets of these blocks. The policy forces customers to route mail through the ISP's own relays, which the provider can monitor and rate-limit. On our side, port 25 is deliberately not exposed on primary mail systems. This ensures every inbound message passes through our dedicated spam and virus filtering gateways rather than allowing direct unauthenticated delivery. For customers this means authenticated submission on alternate ports is required for reliable, reputation-protected sending from your hosted domains and applications.

#Supported SMTP Ports

  • 23 (TLS supported / available) 26 (TLS supported / available) 465 (SSL required) 587 (TLS supported / available) 2025 (TLS supported / available) 2525 (TLS supported / available) 6025 (TLS supported / available) 6465 (SSL required) 8080 (TLS supported / available)

We have published this wide range of ports because some ISPs are beginning to block 26 and 2525 in addition to the standard 25. Each port supports the indicated encryption method. Ports marked SSL required expect an implicit SSL handshake immediately upon connection. Ports marked TLS supported expect a STARTTLS command after the initial plain-text greeting. Using the correct security setting for the chosen port is essential for a successful connection.

We recommend using 465 (SSL required) first then 587 (TLS supported / available) to send mail. If these do not work, try using any of the other ports we have available. In all cases you must authenticate with a valid mailbox username and password before sending. When configuring desktop clients, mobile devices, or server-side code, enter your assigned mail server hostname, select the port, and match the encryption type exactly. Incorrect encryption settings are the most frequent cause of connection failures on these ports.

csharp 
using System.Net;
using System.Net.Mail;

public void SendTestEmail()
{
    var mail = new MailMessage();
    mail.From = new MailAddress("user@yourdomain.com");
    mail.To.Add("recipient@example.com");
    mail.Subject = "SMTP Port Test";
    mail.Body = "This message was sent using an alternate port.";

    using (var smtp = new SmtpClient("mail.yourdomain.com", 465))
    {
        smtp.EnableSsl = true;
        smtp.Credentials = new NetworkCredential("user@yourdomain.com", "password");
        smtp.Send(mail);
    }
}

#Troubleshooting Connection Issues

  • Verify the mail server hostname matches the one provided in your account control panel. Confirm the encryption setting matches the port: use implicit SSL for 465 and 6465; use STARTTLS for all others. Test ports sequentially if the preferred ones fail; some ISPs block additional common alternates. Ensure credentials are correct and that the mailbox exists and is active. Check local firewalls, antivirus, or corporate proxies that may interfere with non-standard ports. Use PowerShell Test-NetConnection or similar tools to confirm TCP reachability on the chosen port.

Because ISPs continue to tighten restrictions on legacy and alternate SMTP ports, the multiple options we maintain maximize the chance of finding an unblocked path. Most customers achieve immediate success with port 465 or 587. When writing code or configuring services, always store the port and encryption settings in configuration files so they can be changed quickly without recompiling. This practice is especially useful for ASP.NET applications and scheduled tasks that send transactional or notification emails.

#Practical Takeaway

Begin with port 465 using SSL, then fall back to 587 with TLS if needed. Update your email client, .NET SmtpClient code, or web application configuration accordingly and test delivery to external addresses. This keeps your mail flow independent of ISP SMTP servers and preserves proper domain authentication. For related steps on mailbox creation, DKIM setup, or web.config mailSettings examples, consult the email configuration section in the control panel documentation.