Why are ports 25 and 465 blocked on my server?

To prevent abuse and protect our network reputation, Cubepath blocks outbound SMTP ports 25 and 465 by default on all new cloud servers.

Unfortunately, email spammers and fraudulent actors frequently attempt to misuse cloud infrastructure to send spam or malicious emails. This is a common issue across the cloud hosting industry, and blocking these ports by default is a widely adopted best practice.

Why does Cubepath block these ports?

We apply this restriction to:

  • Prevent spam and abuse
  • Protect IP reputation and deliverability
  • Ensure network stability and long-term service quality

We want to build trust with new customers before enabling direct SMTP email sending.

When can ports 25 and 465 be unblocked?

Once your account has:

  • Been active for at least one billing cycle
  • Successfully paid the first invoice

You may submit a request to unblock ports 25 and/or 465.

Each request is reviewed case by case, and must include:

  • A clear description of the intended use case
  • The software or service that will use SMTP
  • Confirmation that the usage complies with anti-spam policies

Cubepath reserves the right to approve or deny requests based on risk assessment.

Recommended alternative: Port 587

As an alternative, we strongly recommend using port 587 for sending emails through external mail delivery services (such as transactional email providers).

✔ Port 587 is not blocked ✔ No special request is required ✔ This is the industry-recommended submission port for SMTP

Important notes about account-based blocking

Port blocking is enforced per account.

If a server is transferred to another project or account:

  • The port-blocking rules of the new account owner will apply
  • If the new owner does not have ports 25/465 unblocked, the ports will be blocked again

Before transferring a server that relies on SMTP ports, ensure that the destination account has the required ports enabled.

Need help?

If you believe your use case requires direct SMTP access, please contact our support team with detailed information, and we will be happy to review your request.