mail-server/dovecot.nix: automatically subscribe to new mailboxes

[eqyiel]

When a mailbox is created by sieve or is delivered to directly by IMAP commands, created IMAP folders are not subscribed to by dovecot. These configuration options change that.

Before:

$ doveconf | grep -e '^lda'                                                                                       
lda_mailbox_autocreate = no
lda_mailbox_autosubscribe = no
lda_original_recipient_header =

After:

$ doveconf | grep -e '^lda'
lda_mailbox_autocreate = yes
lda_mailbox_autosubscribe = yes
lda_original_recipient_header =

Despite being prefixed with lda (local delivery agent) and the fact that we are using lmtp for virtual users, I believe this has an effect because:

• it worked for me (subscribed to mailbox 'GitHub' like in the sieve example)
• I see this line in the logs: Nov 21 08:36:25 maher.fyi dovecot[15936]: lmtp(ruben@maher.fyi): Debug: GitHub: Mailbox opened because: lib-lda delivery

[r-raymond]

Thanks alot. I'll try to write a test for the sieves as soon as I find some time.