AuthSMTP SMTP port guide
SMTP Port 2525: Alternative STARTTLS Submission
Use port 2525 with STARTTLS as an AuthSMTP alternative when ports 465 or 587 are unavailable on the current network. It may help on restricted networks, but it cannot guarantee a connection.
Quick answer
- SMTP port
2525- Connection security
- STARTTLS
- Authentication
- Required
- AuthSMTP hostname
- Use the server supplied to your account, normally
mail.authsmtp.com
Do not select implicit SSL/TLS for port 2525.
What SMTP port 2525 means
Port 2525 is widely offered by email service providers as an alternative submission port, but it is not an IETF-assigned SMTP submission port. The IANA service-name and port registry assigns port 2525 to another service.
Support for SMTP on port 2525 is therefore provider-specific. Always confirm that your SMTP provider accepts it and which encryption mode it expects.
Using port 2525 with AuthSMTP
AuthSMTP accepts authenticated submission on port 2525 with STARTTLS. It is a useful alternative when a provider, firewall or local policy blocks the standard submission ports, but any network administrator can also block port 2525.
Use the exact SMTP hostname and credentials shown in your AuthSMTP Control Panel. The hostname is normally mail.authsmtp.com. If your application offers separate SSL/TLS and STARTTLS choices, select STARTTLS.
For application-specific screens, see the AuthSMTP setup guides. If a connection succeeds but mail is rejected, follow the troubleshooting guide to check credentials, account status and authorised sender addresses.
Troubleshoot port 2525
- Confirm the security mode is STARTTLS, not implicit SSL/TLS.
- Make sure authentication is enabled and the AuthSMTP username and password are entered exactly.
- Use the port checker to test the current network; port 2525 is an alternative, not a way to bypass network policy.
- Ask the network administrator whether outbound port 2525 is permitted if the connection times out.
- Try port 587 with STARTTLS or port 465 with implicit TLS if those ports are available.
A successful port test only confirms that a connection can be opened. It does not validate the account password, sender authorisation or the application configuration.
Compare SMTP submission ports
| Port | Security mode | Typical use |
|---|---|---|
| 465 | Implicit TLS | Secure submission where TLS starts immediately |
| 587 | STARTTLS | Standards-based authenticated message submission |
| 2525 (this guide) | STARTTLS | Provider-specific alternative when standard ports are unavailable |
Port 25 is primarily used for mail-server delivery and is frequently restricted on access networks. For an email application or website submitting mail to AuthSMTP, prefer 587 with STARTTLS or 465 with implicit TLS; use 2525 with STARTTLS when an alternative is needed.