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105 lines
4.8 KiB
Markdown
105 lines
4.8 KiB
Markdown
---
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title: 'Advanced | Email Filtering with Sieve'
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---
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## User-Defined Sieve Filters
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[Sieve](http://sieve.info/) allows to specify filtering rules for incoming emails that allow for example sorting mails into different folders depending on the title of an email.
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There are global and user specific filters which are filtering the incoming emails in the following order:
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- Global-before -> User specific -> Global-after
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Global filters are applied to EVERY incoming mail for EVERY email address.
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To specify a global Sieve filter provide a `docker-data/dms/config/before.dovecot.sieve` or a `docker-data/dms/config/after.dovecot.sieve` file with your filter rules.
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If any filter in this filtering chain discards an incoming mail, the delivery process will stop as well and the mail will not reach any following filters (e.g. global-before stops an incoming spam mail: The mail will get discarded and a user-specific filter won't get applied.)
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To specify a user-defined Sieve filter place a `.dovecot.sieve` file into a virtual user's mail folder (e.g. `/var/mail/example.com/user1/home/.dovecot.sieve`). If this file exists dovecot will apply the filtering rules.
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It's even possible to install a user provided Sieve filter at startup during users setup: simply include a Sieve file in the `docker-data/dms/config/` path for each user login that needs a filter. The file name provided should be in the form `<user_login>.dovecot.sieve`, so for example for `user1@example.com` you should provide a Sieve file named `docker-data/dms/config/user1@example.com.dovecot.sieve`.
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An example of a sieve filter that moves mails to a folder `INBOX/spam` depending on the sender address:
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!!! example
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```sieve
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require ["fileinto", "reject"];
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if address :contains ["From"] "spam@spam.com" {
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fileinto "INBOX.spam";
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} else {
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keep;
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}
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```
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!!! warning
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That folders have to exist beforehand if sieve should move them.
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Another example of a sieve filter that forward mails to a different address:
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!!! example
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```sieve
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require ["copy"];
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redirect :copy "user2@not-example.com";
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```
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Just forward all incoming emails and do not save them locally:
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!!! example
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```sieve
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redirect "user2@not-example.com";
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```
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You can also use external programs to filter or pipe (process) messages by adding executable scripts in `docker-data/dms/config/sieve-pipe` or `docker-data/dms/config/sieve-filter`. This can be used in lieu of a local alias file, for instance to forward an email to a webservice. These programs can then be referenced by filename, by all users. Note that the process running the scripts run as a privileged user. For further information see [Dovecot's wiki](https://wiki.dovecot.org/Pigeonhole/Sieve/Plugins/Pipe).
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```sieve
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require ["vnd.dovecot.pipe"];
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pipe "external-program";
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```
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For more examples or a detailed description of the Sieve language have a look at [the official site](http://sieve.info/examplescripts). Other resources are available on the internet where you can find several [examples](https://support.tigertech.net/sieve#sieve-example-rules-jmp).
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## Automatic Sorting Based on Subaddresses
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It is possible to sort subaddresses such as `user+mailing-lists@example.com` into a corresponding folder (here: `INBOX/Mailing-lists`) automatically.
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```sieve
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require ["envelope", "fileinto", "mailbox", "subaddress", "variables"];
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if envelope :detail :matches "to" "*" {
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set :lower :upperfirst "tag" "${1}";
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if mailboxexists "INBOX.${1}" {
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fileinto "INBOX.${1}";
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} else {
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fileinto :create "INBOX.${tag}";
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}
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}
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```
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## Manage Sieve
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The [Manage Sieve](https://doc.dovecot.org/admin_manual/pigeonhole_managesieve_server/) extension allows users to modify their Sieve script by themselves. The authentication mechanisms are the same as for the main dovecot service. ManageSieve runs on port `4190` and needs to be enabled using the `ENABLE_MANAGESIEVE=1` environment variable.
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!!! example
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```yaml
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# compose.yaml
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ports:
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- "4190:4190"
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environment:
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- ENABLE_MANAGESIEVE=1
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```
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All user defined sieve scripts that are managed by ManageSieve are stored in the user's home folder in `/var/mail/example.com/user1/home/sieve`. Just one Sieve script might be active for a user and is sym-linked to `/var/mail/example.com/user1/home/.dovecot.sieve` automatically.
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!!! note
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ManageSieve makes sure to not overwrite an existing `.dovecot.sieve` file. If a user activates a new sieve script the old one is backed up and moved to the `sieve` folder.
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The extension is known to work with the following ManageSieve clients:
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- **[Sieve Editor](https://github.com/thsmi/sieve)** a portable standalone application based on the former Thunderbird plugin.
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- **[Kmail](https://kontact.kde.org/components/kmail/)** the mail client of [KDE](https://kde.org/)'s Kontact Suite.
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