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docs(spf): added basic spf guide

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Jon Lockwood
2022-02-17 13:16:52 +09:30
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---
title: SPF configuration
Description: How to configure SPF for No Fuss Computings docker mail server.
---
Sender Policy Framework (SPF) is defined in [RFC7208, Sender Policy Framework (SPF) for Authorizing Use of Domains in Email](https://datatracker.ietf.org/doc/html/rfc7208).
DNS SPF text record example:
``` text
IN TXT "v=spf1 mx a ip4:192.168.0.100 ip6:2001:ef3:2911::/64"
" a:mail.example.org a:mail2.example.org -all"
```
1. `v=spf1` Version attribute. only v1 available.
2. `mx` `a` DNS record type. This indicated that `mx` and `a` records within the domain are authorized senders.
3. `ip4:192.168.0.100` indicates that an ipv4 address as specified is authorized as a sender.
4. `ip6:2001:ef3:2911::/64` Sepcifies that an ipv6 subnet is authorized as a sender
5. `-all` specifies a fail if the sender doesn't match what is specified in the record. other valid qualifiers are "+" pass, "-" fail, "~" softfail, "?" neutral
!!! tip
To allow only specified MX DNS records to be the only specified senders, create a record as follows:
``` text
IN TXT "v=spf1 mx -all"
```
If your MX servers only receive mail, then this option is not suitable. you'll have to use the hostname of the receiving server.
``` text
IN TXT "v=spf1 a:mail.example.org -all"
```