Embeding a path in address extensions

[@lbutlr]

I generate bcc backups with the pattern

backups+DATE.user.domain.tld at myBackupDomain.tld

(for example, backups+20170908.kremels.kreme.com at myBackupDomain.tld)

This puts mail in …/.20170908.kremels.kreme.com/new

What I would like to do is get the expansion to generate the following path

…/.20170908/.kremels.kreme.com/new

Of course the date changes everyday, but it will always be numeric if that helps.

dovecot get the mail from postfix:

dovecot    unix  -       n       n       -       -       pipe flags=DRhu
    user=vpopmail:vchkpw argv=/usr/local/libexec/dovecot/dovecot-lda -f
    ${sender} -d ${user}@${nexthop} -m ${extension} -a ${original_recipient}

Would it make more sense (or is it even possible) to split the extension in postfix or to do something with sieve? Or is there a character I can use in the extension that tells dovecot to create a path?

Even though I am using a maildir structure for the backups, this "account" never accesses the mail via a MUA, only via the command line when an admin has to restore an email, so it would be much easier to deal with this with daily subfolders.

Or, maybe I make the admins use an MUA? If so, I should replace most of these .'s with dashes… 


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