Networking
What is Port 25?
Port 25 is the TCP port used for server-to-server SMTP mail delivery. Most hosting providers block it permanently to limit spam, which makes self-hosted mail impossible on much of the market. It is open by default on every OnionVPS instance.
Why Port 25 matters
Most hosting providers block it permanently to limit spam, which makes self-hosted mail impossible on much of the market. It is open by default on every OnionVPS instance.
Port 25 in practice
When you run a mail server, Port 25 is the first thing you test after binding your MTA. Run `ss -ltn` and confirm it's listening. Then send a test message from an external host. If your provider blocks the port, mail sits in the queue and your logs show connection timeouts. OnionVPS leaves it open by default, so you can skip the provider support ticket that eats a day on other hosts. Miss this check and you'll debug silent delivery failures for hours.
What people get wrong about Port 25
The common error is treating outbound Port 25 as the same as inbound. Many providers block only outbound, so you can receive mail but cannot send it. Correction: test both directions. Send a message to an external mailbox and watch the queue. On OnionVPS, both directions are open, so a full `telnet` test works from day one.
Port 25 — common questions
Is Port 25 open on my OnionVPS instance?
Yes, Port 25 is open by default on every OnionVPS instance. You can verify with `ss -ltn` after boot or send a test message to an external address. We do not filter server-to-server SMTP traffic, so your MTA will work out of the box.
Why do most hosts block Port 25?
Most providers block Port 25 permanently to limit spam. Since SMTP is unauthenticated and historically abused, they restrict it to force outbound mail through their own relays. OnionVPS does not block it, because we trust you to run a proper mail server with responsible outbound controls.
Where Port 25 comes up
- Is outbound port 25 open, so I can run a mail server? Yes, outbound port 25 is open on every OnionVPS instance by default. There is no support ticket, no account-age requirement and no paid unblock. Most provi…
- What makes OnionVPS different from other VPS providers? Four things: no identity verification of any kind, crypto-only payment with no card or bank involved, 138 locations in 116 countries including genuine offs…
- Can I run my own mail server on a VPS? Yes. Port 25 is open, reverse DNS is self-service, and our address space has no spam history. Mailcow or Stalwart give you a complete stack in an evening. …
- A self-hosted mail server that actually reaches the inbox Installing a mail server is easy; being trusted by receivers is not. You need outbound port 25, a PTR record matching your banner hostname, SPF, DKIM and D…
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