How to re-apply Sieve fil­ters to a Dove­cot IMAP inbox

Introduction

Our Dove­cot IMAP email ser­vice user defined mail fil­ter rules using the Man­a­ge­sieve pro­to­col. His Sieve rules auto­mat­i­cally clas­sify the hun­dreds of emails flood­ing his inbox every day. They delete unwanted mes­sages, store oth­ers in dis­tinct fold­ers, set flags and pri­or­i­tize them for later read­ing. A typo in his sieve scripts caused the fil­ters to break. Emails were sent directly to his inbox where now thou­sands of unclas­si­fied newslet­ters and spam mails linger, mak­ing him unable to deter­mine the impor­tant com­mu­ni­ca­tion. We were asked to help him refilter the mes­sages using his fixed Sieve fil­ters.

Example environment

For the sake of this arti­cle, we use `user.name@exam­ple.com` as email inbox. We advice our IMAP user to cre­ate a sub­folder `Refilter` in his email inbox and move all unclas­si­fied emails into this folder.

Our exam­ple Dove­cot email server uses `/var/vmail/[domain]/[user]` as stor­age loca­tion. User-defined cus­tom Sieve scripts are located in a `/var/vmail/[domain]/[user]/.sieve` sym­bolic link that tar­gets the enabled Sieve fil­ter rules file. The inbox folder root is `INBOX`.

Proceedings

In order to re-apply Sieve rules on a Dove­cot IMAP server, newer ver­sions of Dove­cot Pigeon­hole come with the `sieve-fil­ter` tool. It takes the tar­get inbox, the sieve rules to apply, and the inbox folder to apply the rules to as argu­ments:

By default, the `sieve-fil­ter` com­mand runs in sim­u­la­tion mode. To apply any changes, we have to explic­itly enable exe­cu­tion mode by adding the `-e` option, and allow write and delete access to the mail­box by adding the `-W` option. We also want the Sieve scripts to be recom­piled to apply any last changes by the user. So we add the `-C` option to the com­mand (a com­plete ref­er­ence of avail­able options can be found at the Pigeon­hole Dove­cot sieve-fil­ter doc­u­men­ta­tion page):

Con­sid­er­ing that inboxes can grow rather large, and pro­cess­ing thou­sands of mes­sages at a time may put a heavy strain on our live mail server, we may want to run the fil­ter­ing with lower pri­or­ity, only when the sys­tem isn't too busy. There­fore, we addi­tion­ally use the `ion­ice` com­mand with `-c2` for best-effort mode and `-n7` for low­est pri­or­ity:

Wrap it into a Bash script

We don't always want to return to our knowl­edge base when hav­ing to help a mail user to refilter its mes­sages. There­fore, we cre­ated a sim­ple Bash script that just requires the mail user name as argu­ment and does the job for us.

It is using the `doveadm` user lookup com­mand to deter­mine the users' Sieve script loca­tion and mail­box fold­ers:

Which, for exist­ing mail­box users, returns an answer like this:

We are using the `maildir` infor­ma­tion to check for exist­ing mes­sages to process, as well as the `sieve` infor­ma­tion to find the user-defined Sieve rules.

And here is the script as ref­er­ence for our val­ued read­ers `sieve-refilter.sh`: 

Make the script exe­cutable:

Now we can run the script as admin­is­tra­tor or vmail shell user:

Conclusion

The Pigeon­hole `sieve-fil­ter` tool is great for re-run­ning Sieve fil­ter rules on a Dove­cot IMAP inbox folder. We cre­ated a sim­ple script to per­form this oper­a­tion for a sin­gle user.