Port 25 Blocked? Here's How to Fix It
Your server sends nothing and the queue just grows — classic blocked port 25. Here's why it happens and how to get it unblocked.
TL;DR
Most hosts block outbound port 25 by default to stop spam. To send directly you must request an unblock from your provider (after proving legitimate use) or choose a host that allows it. Port 25 is required for MTA-to-MTA delivery.
Why providers block port 25
Compromised servers are a top spam source, so cloud providers (AWS, Google Cloud, many VPS hosts) block outbound 25 by default. It's a spam-prevention measure, not a fault with your setup.
How to confirm it's blocked
From the server, test a connection to a remote mail server on port 25. If it times out but other ports work, 25 is blocked. Tools like MXToolbox help verify reachability.
How to get it unblocked
- Open a support request with your host. Explain your legitimate use case and volume.
- Show compliance: proper SPF/DKIM/DMARC, rDNS and an unsubscribe process build trust.
- Choose an email-friendly host if yours refuses — some specialise in allowing port 25.
What not to do
Don't try to route bulk delivery through port 587 to a relay as a workaround for serious volume — you'll hit limits and lose the reputation control that dedicated IPs give you.
After unblocking
Once 25 is open, set up rDNS, authenticate, and warm up your IP before sending at volume.
AutoPMTA verifies port 25 and your full mail config during install. See pricing.
Key takeaways
- Port 25 is blocked by default on most hosts to curb spam.
- Request an unblock and prove legitimate, compliant use.
- Switch to an email-friendly host if yours refuses.
- Set rDNS, authenticate and warm up after unblocking.
Frequently asked questions
How do I unblock port 25?+
Open a support ticket with your hosting provider requesting outbound port 25 be unblocked. Explain your legitimate use case and show you have proper SPF, DKIM, DMARC and rDNS in place.
Why can't I send email from my VPS?+
The most common reason is that outbound port 25 is blocked by your provider. Until it is unblocked, your MTA cannot deliver mail directly to other servers and the queue will grow.
Can I send bulk email on port 587 instead?+
Port 587 is for authenticated submission to a relay, not direct server-to-server delivery. For self-hosted bulk sending with reputation control, you need outbound port 25 open.