Using virtual folders with younger and index files

[Rob Hoelz]

Hi list,

I just encountered a problem while using dovecot's Virtual plugin with 2.3.0.  I managed to solve the issue,
but I wanted to bring it to the attention of others on the list to see if there exists a better solution, if
I found a bug, or if it's just a matter of updating documentation.

I have a virtual folder to get the most recent two weeks of mails; it looks something like this:

> INBOX
>   all younger 1209600

I made this folder back in October.  Lately, I started to notice that the virtual folder had a surprising amount
of mail in it - I don't get 1,000 e-mails per week!  After some doveadm commands, I realized that e-mails from
October were still present in my virtual folder!  Updating the dovecot-virtual would clear away e-mails older than
two weeks (I needed to actually introduce a change, even if it was just whitespace - just touching the file didn't
update things), and removing the dovecot index file also cleared things away.  In then end, I ended up just telling
dovecot to disable on-disk indexes for that folder.

I created this folder based on the examples on https://wiki.dovecot.org/Plugins/Virtual - I'm wondering if I found a bug
or if that page should be changed to recommend disabling on-disk indexes when using certain search query filters such as
"younger".  If the latter, I can always make the change - just let me know!

-Rob