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Consistency pass, formatting cleanup and fixes, introduce admonitions, add front-matter. --- docs: Add front-matter --- docs: Fix and format links - Some links were invalid (eg files moved or renamed) - Some were valid but had invalid section headers (content removed or migrated) - Some use `http://` instead of `https://` when the website supports a secure connection. - Some already used the `[name][reference]` convention but often with a number that wasn't as useful for maintenance. - All referenced docs needed URLs replaced. Opted for the `[name][reference]` approach to group them all clearly at the bottom of the doc, especially with the relative URLs and in some cases many duplicate entries. - All `tomav` references from the original repo prior to switch to an organization have been corrected. - Minor cosmetic changes to the `name` part of the URL, such as for referencing issues to be consistent. - Some small changes to text body, usually due to duplicate URL reference that was unnecessary (open relay, youtous) - Switched other links to use the `[name][reference]` format when there was a large group of URLs such as wikipedia or kubernetes. Github repos that reference projects related to `docker-mailserver` also got placed here so they're noticed better by maintainers. This also helped quite a bit with `mermaid` external links that are very long. - There was a Github Wiki supported syntax in use `[[name | link]]` for `fetchmail` page that isn't compatible by default with MkDocs (needs a plugin), converted to `[name][reference]` instead since it's a relative link. --- docs: Update commit link for LDAP override script Logic moved to another file, keeping the permalink commit reference so it's unaffected by any changes in the file referenced in future. --- docs: Heading corrections Consistency pass. Helps with the Table of Contents (top-right UI) aka Document Outline. docs: codefence cleanup --- docs: misc cleanup --- docs: Add Admonitions Switches `<details>` usage for collapsible admonitions (`???`) while other text content is switched to the visually more distinct admoniton (`!!!` or `???+`) style. This does affect editor syntax highlighting a bit and markdown linting as it's custom non-standard markdown syntax.
109 lines
4.3 KiB
Markdown
109 lines
4.3 KiB
Markdown
---
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title: 'Best Practices | DKIM'
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---
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DKIM is a security measure targeting email spoofing. It is greatly recommended one activates it. See [the Wikipedia page](https://en.wikipedia.org/wiki/DomainKeys_Identified_Mail) for more details on DKIM.
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## Enabling DKIM Signature
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To enable DKIM signature, **you must have created at least one email account**. Once its done, just run the following command to generate the signature:
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```sh
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./setup.sh config dkim
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```
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After generating DKIM keys, you should restart the mail server. DNS edits may take a few minutes to hours to propagate. The script assumes you're being in the directory where the `config/` directory is located. The default keysize when generating the signature is 4096 bits for now. If you need to change it (e.g. your DNS provider limits the size), then provide the size as the first parameter of the command:
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```sh
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./setup.sh config dkim <keysize>
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```
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For LDAP systems that do not have any directly created user account you can run the following command (since `8.0.0`) to generate the signature by additionally providing the desired domain name (if you have multiple domains use the command multiple times or provide a comma-separated list of domains):
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```sh
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./setup.sh config dkim <key-size> <domain.tld>[,<domain2.tld>]
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```
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Now the keys are generated, you can configure your DNS server with DKIM signature, simply by adding a TXT record. If you have direct access to your DNS zone file, then it's only a matter of pasting the content of `config/opendkim/keys/domain.tld/mail.txt` in your `domain.tld.hosts` zone.
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```console
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$ dig mail._domainkey.domain.tld TXT
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---
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;; ANSWER SECTION
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mail._domainkey.<DOMAIN> 300 IN TXT "v=DKIM1; k=rsa; p=AZERTYUIOPQSDFGHJKLMWXCVBN/AZERTYUIOPQSDFGHJKLMWXCVBN/AZERTYUIOPQSDFGHJKLMWXCVBN/AZERTYUIOPQSDFGHJKLMWXCVBN/AZERTYUIOPQSDFGHJKLMWXCVBN/AZERTYUIOPQSDFGHJKLMWXCVBN/AZERTYUIOPQSDFGHJKLMWXCVBN/AZERTYUIOPQSDFGHJKLMWXCVBN"
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```
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## Configuration using a Web Interface
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1. Generate a new record of the type `TXT`.
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2. Paste `mail._domainkey` the `Name` txt field.
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3. In the `Target` or `Value` field fill in `v=DKIM1; k=rsa; p=AZERTYUGHJKLMWX...`.
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4. In `TTL` (time to live): Time span in seconds. How long the DNS server should cache the `TXT` record.
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5. Save.
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!!! note
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Sometimes the key in `config/opendkim/keys/domain.tld/mail.txt` can be on multiple lines. If so then you need to concatenate the values in the TXT record:
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```console
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$ dig mail._domainkey.domain.tld TXT
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---
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;; ANSWER SECTION
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mail._domainkey.<DOMAIN> 300 IN TXT "v=DKIM1; k=rsa; "
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"p=AZERTYUIOPQSDF..."
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"asdfQWERTYUIOPQSDF..."
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```
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The target (or value) field must then have all the parts together: `v=DKIM1; k=rsa; p=AZERTYUIOPQSDF...asdfQWERTYUIOPQSDF...`
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## Verify-Only
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If you want DKIM to only _verify_ incoming emails, the following version of `/etc/opendkim.conf` may be useful (right now there is no easy mechanism for installing it other than forking the repo):
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```conf
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# This is a simple config file verifying messages only
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#LogWhy yes
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Syslog yes
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SyslogSuccess yes
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Socket inet:12301@localhost
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PidFile /var/run/opendkim/opendkim.pid
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ReportAddress postmaster@my-domain.com
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SendReports yes
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Mode v
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```
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## Debugging
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- [DKIM-verifer](https://addons.mozilla.org/en-US/thunderbird/addon/dkim-verifier): A add-on for the mail client Thunderbird.
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- You can debug your TXT records with the `dig` tool.
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```console
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$ dig TXT mail._domainkey.domain.tld
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---
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; <<>> DiG 9.10.3-P4-Debian <<>> TXT mail._domainkey.domain.tld
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;; global options: +cmd
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;; Got answer:
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;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39669
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;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
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;; OPT PSEUDOSECTION:
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; EDNS: version: 0, flags:; udp: 512
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;; QUESTION SECTION:
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;mail._domainkey.domain.tld. IN TXT
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;; ANSWER SECTION:
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mail._domainkey.domain.tld. 3600 IN TXT "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCxBSjG6RnWAdU3oOlqsdf2WC0FOUmU8uHVrzxPLW2R3yRBPGLrGO1++yy3tv6kMieWZwEBHVOdefM6uQOQsZ4brahu9lhG8sFLPX4MaKYN/NR6RK4gdjrZu+MYSdfk3THgSbNwIDAQAB"
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;; Query time: 50 msec
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;; SERVER: 127.0.1.1#53(127.0.1.1)
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;; WHEN: Wed Sep 07 18:22:57 CEST 2016
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;; MSG SIZE rcvd: 310
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```
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## Switch Off DKIM
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Simply remove the DKIM key by recreating (not just relaunching) the mailserver container.
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