A Quick Overview of SMTP Ports
SMTP (Simple Mail Transfer Protocol) is the standard protocol used to send emails between servers. Depending on the use case and security requirements, different ports are used:
- Port 25 — the original SMTP port, used for server-to-server email relay. Rarely appropriate for application-level sending today.
- Port 587 — the modern standard for authenticated email submission from clients or applications to a mail server.
- Port 465 — originally assigned for SMTPS (SMTP over SSL), now commonly used for implicit TLS connections.
- Port 2525 — an unofficial alternative often used when 587 is blocked, popular with transactional email services.
Each port serves a slightly different role in the email delivery chain, but they all share one thing: they’re high-value targets for abuse.
SMTP Ports on Cloudzy
SMTP ports 25, 587, 465, and 2525 are blocked by default on all Cloudzy servers.
This isn’t an oversight — it’s a deliberate security measure. Open SMTP ports on cloud infrastructure are one of the most common vectors for spam campaigns, phishing operations, and large-scale email abuse. Left unrestricted, a single compromised server can send millions of emails, damage shared IP reputations, and get entire netblocks blacklisted. Preventing that by default is critical for maintaining the integrity of Cloudzy’s network and protecting all users on the platform.
Can They Be Unblocked?
In certain cases, yes — but it’s not guaranteed.
If your use case genuinely requires SMTP access, you can submit a request to Cloudzy’s support team for review. The team will assess the request based on the nature of the workload and other factors. Approval is not automatic, and unblocking is not guaranteed even after review.
The default remains closed. Any exception requires explicit support confirmation.
To submit a request, open a ticket through the Cloudzy support portal.