How to Open Port 25 on Cloud Servers
Port 25 is the standard SMTP port used for server-to-server email delivery. Most cloud providers block it by default on new accounts to prevent spam abuse.
On AWS: Port 25 is blocked at the network level (not the security group level). To request removal, go to AWS Console → Support Center → Create Case → Service Limit Increase → EC2 Port 25 Removal. AWS reviews these requests and may deny them if the account is new or lacks billing history. Approved accounts get port 25 unblocked for specific IP addresses.
On DigitalOcean: By default, all Droplets block outbound port 25. DigitalOcean requires submitting a support ticket with justification (legitimate email server use case). Approval depends on account age and history.
The alternative: buy a pre-configured open port account. Our port 25 open accounts for DigitalOcean (3, 10, 25 Droplets), Linode, IBM, Kamatera, and Atlantic come with port 25 already open — no waiting for approvals. This is the fastest path to a working SMTP server.
Once you have port 25 open, set up Postfix or Exim as your MTA, configure SPF/DKIM/DMARC for your domain, set up reverse DNS, and test with tools like MXToolbox.
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