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59 lines
2.4 KiB
Markdown
59 lines
2.4 KiB
Markdown
---
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title: 'Best Practices | SPF'
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hide:
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- toc # Hide Table of Contents for this page
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---
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From [Wikipedia](https://en.wikipedia.org/wiki/Sender_Policy_Framework):
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!!! quote
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Sender Policy Framework (SPF) is a simple email-validation system designed to detect email spoofing by providing a mechanism to allow receiving mail exchangers to check that incoming mail from a domain comes from a host authorized by that domain's administrators. The list of authorized sending hosts for a domain is published in the Domain Name System (DNS) records for that domain in the form of a specially formatted TXT record. Email spam and phishing often use forged "from" addresses, so publishing and checking SPF records can be considered anti-spam techniques.
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!!! seealso
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For a more technical review: https://github.com/internetstandards/toolbox-wiki/blob/master/SPF-how-to.md
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## Add a SPF Record
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To add a SPF record in your DNS, insert the following line in your DNS zone:
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```txt
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; MX record must be declared for SPF to work
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domain.com. IN MX 1 mail.domain.com.
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; SPF record
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domain.com. IN TXT "v=spf1 mx ~all"
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```
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This enables the _Softfail_ mode for SPF. You could first add this SPF record with a very low TTL.
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_SoftFail_ is a good setting for getting started and testing, as it lets all email through, with spams tagged as such in the mailbox.
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After verification, you _might_ want to change your SPF record to `v=spf1 mx -all` so as to enforce the _HardFail_ policy. See http://www.open-spf.org/SPF_Record_Syntax for more details about SPF policies.
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In any case, increment the SPF record's TTL to its final value.
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## Backup MX, Secondary MX
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For whitelisting a IP Address from the SPF test, you can create a config file (see [`policyd-spf.conf`](https://www.linuxcertif.com/man/5/policyd-spf.conf)) and mount that file into `/etc/postfix-policyd-spf-python/policyd-spf.conf`.
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**Example:**
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Create and edit a `policyd-spf.conf` file here `/<your docker-mailserver dir>/config/postfix-policyd-spf.conf`:
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```conf
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debugLevel = 1
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#0(only errors)-4(complete data received)
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skip_addresses = 127.0.0.0/8,::ffff:127.0.0.0/104,::1
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# Preferably use IP-Addresses for whitelist lookups:
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Whitelist = 192.168.0.0/31,192.168.1.0/30
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# Domain_Whitelist = mx1.mybackupmx.com,mx2.mybackupmx.com
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```
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Then add this line to `docker-compose.yml`:
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```yaml
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volumes:
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- ./config/postfix-policyd-spf.conf:/etc/postfix-policyd-spf-python/policyd-spf.conf
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```
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