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:
- Windows: Download from http://www.jetmore.org/john/code/swaks/
- Mac:
brew install swaks
or download from the website - Linux:
apt-get install swaks
oryum install swaks
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.