This guide provides command line instructions to test SMTP connectivity to outbound.mailhop.org and troubleshoot communication issues.

What a Successful Connection Looks Like:

When testing connectivity, you should see an SMTP banner response like this:

Command:  nc outbound.mailhop.org 25
Response:  220 outbound4.ore.mailhop.org ESMTP

This confirms the port is open and the SMTP service is responding properly.

Available SMTP Ports:

  • Port 25: Standard SMTP (may be blocked by ISPs)
  • Port 587: Submission port with STARTTLS
  • Port 2525: Alternative submission port
  • Port 465: SMTP over SSL/TLS

Windows Commands

Test port connectivity using Telnet:

telnet outbound.mailhop.org 25
telnet outbound.mailhop.org 587
telnet outbound.mailhop.org 2525
telnet outbound.mailhop.org 465

Test port connectivity using PowerShell:

Use this method if telnet is not available on the system:

Test-NetConnection -ComputerName outbound.mailhop.org -Port 25
Test-NetConnection -ComputerName outbound.mailhop.org -Port 587
Test-NetConnection -ComputerName outbound.mailhop.org -Port 2525
Test-NetConnection -ComputerName outbound.mailhop.org -Port 465

Mac/Linux Commands

Test port connectivity using Telnet:

telnet outbound.mailhop.org 25
telnet outbound.mailhop.org 587
telnet outbound.mailhop.org 2525
telnet outbound.mailhop.org 465

Test port connectivity using Netcat (nc):

nc -zv outbound.mailhop.org 25
nc -zv outbound.mailhop.org 587
nc -zv outbound.mailhop.org 2525
nc -zv outbound.mailhop.org 465

SWAKS (Swiss Army Knife for SMTP)

SWAKS is a comprehensive SMTP testing tool that provides detailed protocol-level testing capabilities.

Installation:

Basic SWAKS Test Examples:

Test basic connectivity and SMTP capability:

swaks --to test@example.com --from sender@example.com --server outbound.mailhop.org --port 25

Test with authentication (if required):

swaks --to test@example.com --from sender@example.com --server outbound.mailhop.org --port 587 --auth --auth-user username --auth-password password

Test TLS/SSL connectivity:

For STARTTLS (ports 25, 587, 2525):

swaks --to test@example.com --from sender@example.com --server outbound.mailhop.org --port 587 --tls

For SSL/TLS (port 465):

swaks --to test@example.com --from sender@example.com --server outbound.mailhop.org --port 465 --tlsc

Test all ports with verbose output:

Port 25 (standard SMTP):

swaks --to test@example.com --from sender@example.com --server outbound.mailhop.org --port 25 -v

Port 587 (submission with STARTTLS):

swaks --to test@example.com --from sender@example.com --server outbound.mailhop.org --port 587 --tls -v

Port 2525 (alternative submission with STARTTLS):

swaks --to test@example.com --from sender@example.com --server outbound.mailhop.org --port 2525 --tls -v

Port 465 (SMTP over SSL/TLS):

swaks --to test@example.com --from sender@example.com --server outbound.mailhop.org --port 465 --tlsc -v

Expected Results

Successful Connection:

You should see the SMTP banner, typically something like:

220 outbound.mailhop.org ESMTP...

Common Issues:

  • Connection refused: Port is blocked or service isn't running on that port
  • Timeout: Network connectivity issue or firewall blocking the connection
  • DNS resolution failure: Unable to resolve outbound.mailhop.org

Troubleshooting Tips

  • Start with basic telnet/nc tests to verify port accessibility
  • Use SWAKS for comprehensive SMTP protocol testing
  • Test from different network locations if possible
  • Check firewall settings on both client and server sides
  • Verify DNS resolution: nslookup outbound.mailhop.org
  • Many ISPs block port 25 - try alternative ports 587, 2525, or 465

Note: The telnet and nc tests confirm basic port accessibility, while SWAKS provides comprehensive SMTP protocol testing including authentication and encryption capabilities.