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Network: IPv4, IPv6, reverse DNS and mail ports

Your VPS addresses, setting reverse DNS yourself, and how to request unblocking of the mail ports.

4 min read

On this page

The Network section of your VPS shows its IP addresses, the reverse DNS entry for each address and the state of the mail ports.

IP addresses

Every VPS has one IPv4 and one IPv6 address. Both are listed under IP addresses and in the Overview. The button next to an address copies it.

The addresses are already configured in the system. Check on the server with:

bash
ip -br addr
ping -c 3 -6 2606:4700:4700::1111

How to use IPv6 properly in services and the firewall: IPv6 and reverse DNS.

Setting reverse DNS

Reverse DNS (PTR) answers the question "which name belongs to this IP?". It matters most for mail servers: many receivers reject mail from addresses without a matching PTR.

  1. First create an A record (IPv4) or AAAA record (IPv6) in your domain's DNS zone that points to the server's address, e.g. mail.example.com. For domains with us: DNS records.
  2. Under IP addresses, click rDNS next to the address.
  3. Enter the fully qualified hostname, e.g. mail.example.com, and save.

Saving an empty field removes the entry. Check after a few minutes whether it worked:

bash
dig -x YOUR-IPV4 +short

If your hostname comes back, it is set.

Mail ports

Outgoing ports 25, 465 and 587 are blocked. The reason is spam: a single compromised or misconfigured server can send thousands of emails in a short time. Then our addresses end up on blocklists, and mail from every customer stops arriving.

Incoming mail is not affected. And for mail from your application you often do not need these ports at all: many mail providers also accept mail on another port or through an HTTP API. What works well is in Sending mail from your server.

Requesting unblocking

For your own mail server you can request unblocking. Under Network, at Mail ports, fill in:

FieldExample
Mail server softwarePostfix, mailcow, Mailu
Mail server hostnamemail.example.com. Should be set as reverse DNS on the IPv4.
What are the emails for?Briefly describe your project and who receives the emails.
Expected volumee.g. 200 emails per day

Then confirm the rules (no spam, no unsolicited advertising, blocked again in case of abuse) and click Send request. The request becomes a ticket. Any questions come there; Go to ticket takes you straight to it. There is no fixed processing time.

What you see afterwards

  • The mail ports are open for this server. With Block again you close them yourself.
  • Your last request was rejected or The unblocking was revoked, with a reason. You can send a new request.
  • Your plan does not block the mail ports. Then there is nothing to do.

Spam blocklists

Below, Spam blocklists shows whether your addresses are on known blocklists. Check now queries again. For every list you see not listed, listed or no response, and whether your address's PTR points back. If an address is listed, Delist takes you to the list's page. If it says "rates the whole network", the entry does not only concern your address.

Next steps

If saving reverse DNS does not work, open a ticket with the address and hostname.