First, I have to say this. After configuring everything correctly - and that means *everything* correctly - Dovecot replication Just Works. I'm not sure how (yes I do - Timo & Co. Magic) - but it does. Real-time new sync is near instantaneous.

Now the problem. Or the background for the problem. My primary server uses sdbox for primary storage, mdbox for archival storage, and fts-solr. I spun up a second server, using sdbox, mdbox, and fts-flatcurve. My namespaces are as defined below. As best I can tell (based on diff comparing two 'doveconf -n' outputs) my namespaces are the same on both servers.

namespace archives {

  list = children

  location = mdbox:/var/mail/%d/%n/Archives/mdbox

  mailbox Unsorted {

    auto = no

    special_use = \Archive

  }

  prefix = INBOX/Archives/

  separator = /

  subscriptions = no

  type = private

}

namespace inbox {

  alias_for =

  hidden = no

  inbox = yes

  list = yes

  location =

  mailbox "Deleted Messages" {

    auto = no

    autoexpunge = 30 days

    special_use = \Trash

  }

  mailbox Drafts {

    auto = subscribe

    special_use = \Drafts

 }

  mailbox Sent {

    auto = subscribe

    special_use = \Sent

  }

  mailbox Trash {

    auto = subscribe

    autoexpunge = 30 days

    special_use = \Trash

  }

  prefix = INBOX/

  separator = /

  subscriptions = no

  type = private

}

namespace lists {

  list = children

  location = mdbox:/var/mail/%d/%n/Lists/mdbox

  prefix = INBOX/Lists/

  separator = /

  subscriptions = no

  type = private

}

namespace subscriptions {

  hidden = yes

  list = no

  location =

  prefix =

  separator = /

  subscriptions = yes

  type = private

}

namespace usershares {

  list = yes

  location = sdbox:/var/mail/%%d/%%n/sdbox:NO-NOSELECT

  prefix = INBOX/shared/%%d/%%n/

  separator = /

  subscriptions = no

  type = shared

}

namespace virtual {

  list = children

  location = virtual:/var/mail/%d/%n/virtual

  mailbox Flagged {

    comment = All my flagged messages

    special_use = \Flagged

  }

  prefix = INBOX/virtual/

  separator = /

  subscriptions = no

}

I also have:

plugin {

  mailbox_alias_new = Sent Messages

  mailbox_alias_new2 = Sent Items

  mailbox_alias_new3 = Deleted Messages

  mailbox_alias_old = Sent

  mailbox_alias_old2 = Sent

  mailbox_alias_old3 = Trash

}

This setup worked fine with my single server. Then I enabled replication - just on the primary. Dsync went to work (it seemed to take forever for the initial sync but that's what happens with large mailboxes and slow internet connections).

The problem came up with certain subfolders. And I believe it only happens with subfolders that have spaces in their names. I had two user's mailboxes (under Sent), one of which had a "Sent Messages" symlink alias for "Sent", that started generating tens or hundreds of duplicates during sync. Fortunately those subfolders only had a few mails in them. But I had trees looking like:

[...] (below is under /var/mail/domain/user/sdbox/mailboxes/Sent/)

Proposal Requests-temp-c6e003375e64a961c93d00009db5accb-temp-1-temp-f80b1a00ce9aa961a86-temp-2

Proposal Requests-temp-c6e003375e64a961c93d00009db5accb-temp-1-temp-f80b1a00ce9aa961a86-temp-3

Proposal Requests-temp-c6e003375e64a961c93d00009db5accb-temp-2-temp-023fa4271c9ca9611ade0400b88bfabe

Proposal Requests-temp-c6e003375e64a961c93d00009db5accb-temp-2-temp-023fa4271c9ca9611ad-temp-1

Proposal Requests-temp-c6e003375e64a961c93d00009db5accb-temp-2-temp-1

Proposal Requests-temp-c6e003375e64a961c93d00009db5accb-temp-2-temp-2

Proposal Requests-temp-c6e003375e64a961c93d00009db5accb-temp-2-temp-2-temp-1-temp-1

Proposal Requests-temp-c6e003375e64a961c93d00009db5accb-temp-2-temp-3

Proposal Requests-temp-c6e003375e64a961c93d00009db5accb-temp-2-temp-4

Proposal Requests-temp-c6e003375e64a961c93d00009db5accb-temp-2-temp-5

Proposal Requests-temp-c6e003375e64a961c93d00009db5accb-temp-2-temp-e2aa0f35c99ba961356500009db5accb

[...]

I kept stopping, cleaning up the folders, and re-starting - and they kept regenerating. I tried renaming the folders to eliminate the spaces and I think that helped in one case - for the others I just moved the folders outside of the mail area completely to let the sync finish.

Now that it's been stable for a day or two - I enabled sync in the other direction. And after setting *all* the required parameters instead of just most of them...it's working. But...I'm nervous about moving the problem folders back over. I will say, if it makes any difference, my primary server *was* running version 2.3.13 and I just updated it to 2.3.17. The remote is also 2.3.17.

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