What is SPF?
SPF is a DNS record listing which servers are authorised to send mail for a domain. It is the first of three records receivers check. Without it, mail from a new server is treated as suspicious by default.
Why SPF matters
It is the first of three records receivers check. Without it, mail from a new server is treated as suspicious by default.
SPF in practice
When running a server, SPF means publishing a TXT record in DNS that lists every host allowed to send mail for your domain. You add your VPS's IPv4, your IPv6 subnet, and any third-party senders like a mailing list. Check it with dig TXT domain. Get it wrong—miss a host, forget the IPv6—and your mail lands in spam or bounces. Testing each new outbound mail server before you send is the habit that saves you.
What people get wrong about SPF
A common mistake is including only IPv4 addresses in the SPF record, forgetting the IPv6 address that the server also uses. Mail receivers check both address families, and if your VPS sends via IPv6 but the record only lists IPv4, the SPF check fails. Correct the record to list every IP the server actually sends from, both v4 and v6.
SPF — common questions
How do I check my SPF record?
Use a DNS lookup tool, for example running dig TXT yourdomain.com in a terminal. Look for a line starting with v=spf1. That shows the current record. Verify it includes all your mail servers' IP addresses.
What does SPF failure mean?
When a receiving server gets mail from your domain, it checks your SPF record. If the sending server's IP is not listed, the check fails. The receiving server often marks the mail as spam or rejects it. Fix your record to include that IP.
Where SPF comes up
- 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…
- 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…