System & VPS Prerequisites
Server, network, and DNS requirements for an EmitMail deployment.
Before deploying EmitMail, check that your server meets these baseline requirements:
Linux Server (VPS or Dedicated Host)
- OS: Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, or Debian 12 recommended.
- Hardware: Start with at least 1 vCPU, 2 GB RAM, and 20 GB SSD; actual needs depend on message volume and retention.
- IP Address: A static public IP address is strongly recommended. Check its reputation and whether your provider allows mail server traffic.
SMTP Network Access
Inbound TCP port 25 is needed to receive internet email. Outbound TCP port 25 is needed for direct-to-recipient delivery. Hosting providers may restrict either direction; check the current policy for your plan and region.
Check provider and firewall rules
If port 25 is restricted, ask your hosting provider whether it can be enabled. Also check the provider firewall/security group and the server firewall.
Configure DNS (Any DNS Provider)
Ensure your root domain (e.g. yourdomain.com) is managed under an active DNS provider (such as Cloudflare, AWS Route 53, Namecheap, Porkbun, or Google Cloud DNS) so you can configure custom TXT, MX, and A records.
Important Proxy / CDN Notice
If your DNS provider offers an HTTP reverse proxy, mail hostnames and MX targets must resolve directly to the mail server. An HTTP proxy does not proxy SMTP. Follow the hostnames and values in the dashboard DNS checklist.
Verifying Port 25 Connectivity
To test whether outbound Port 25 is open from your VPS, run this test command:
telnet gmail-smtp-in.l.google.com 25
# or using netcat:
nc -zv gmail-smtp-in.l.google.com 25Expected successful response:
Connection to gmail-smtp-in.l.google.com 25 port [tcp/smtp] succeeded!
220 mx.google.com ESMTPIf the connection fails or times out, check provider restrictions, firewall rules, and network connectivity. A timeout alone does not identify which layer blocked the connection.