Hi,

this setting might work. The default namespace "inbox" is managing INBOX and defines Special-Use folders on the same hierarchic level as INBOX. There is an extra namespace "4archives" which defines Archive as a mailbox on the same level as INBOX but stored on a different location. Set mailbox attribute auto to your liking.


namespace inbox {
type = private
disabled = no
hidden = no
list = yes
ignore_on_failure = no
inbox = yes
location =
prefix =
subscriptions = yes
separator = /

mailbox Drafts {
special_use = \Drafts
auto = subscribe
}
mailbox Junk {
special_use = \Junk
auto = subscribe
}
mailbox Spam {
special_use = \Junk
auto = no
}
mailbox spam {
special_use = \Junk
auto = no
}
mailbox Deleted {
special_use = \Trash
auto = subscribe
}
mailbox Trash {
special_use = \Trash
auto = no
}
mailbox Wastebasket {
special_use = \Trash
auto = no
}
  mailbox Sent {
special_use = \Sent
auto = subscribe
}
mailbox "Sent Messages" {
special_use = \Sent
auto = no
}
mailbox "Sent Mail" {
special_use = \Sent
auto = no
}
mailbox "Tasks" {
# This mailbox has no official RFC 6154 or RFC 8457 Special-Use entry
auto = subscribe
}
}

namespace 4archives {
type = private
disabled = no
hidden = no
list = yes
ignore_on_failure = no
inbox = no
location = mbox:/home/mail-archive/%u/Archive/:CONTROL=/home/mail-archive/%u/Archive/control:INDEX=/home/mail-archive/%u/Archive/index:LAYOUT=maildir++
prefix =
subscriptions = yes
separator = /
mailbox Archive {
auto = create
autoexpunge = 0
autoexpunge_max_mails = 0
comment =
driver =
special_use = \Archive
}
mailbox Archives {
auto = no
autoexpunge = 0
autoexpunge_max_mails = 0
comment =
driver =
special_use = \Archive
}
mailbox "Archived Messages" {
auto = no
autoexpunge = 0
autoexpunge_max_mails = 0
comment =
driver =
special_use = \Archive
}
mailbox "Archived mail" {
auto = no
autoexpunge = 0
autoexpunge_max_mails = 0
comment =
driver =
special_use = \Archive
}
}



On Fri, 2019-01-04 at 12:06 +0100, Marc Roos wrote:
 

Where is a manual describing how to do this? Archive tree on different 
storage?

├── Archive/Archives/Archived Messages/Archived mail <- need to store 
messages in root folder also
│   ├── 2017
│   │   ├── projects
│   │   │   ├── project
│   │   │   ├── project1
│   │   │   ├── project2
│   │   │   ├── project3
│   │   │   ├── project4
│   │   │   └── project5
│   │   └── Sent Messages
│   ├── 2018
│   │   ├── project1
│   │   ├── project2
│   │   ├── project3
│   │   ├── project4
│   │   ├── project5
│   │   └── Sent
│   └── 2019
│       ├── projectA
│       └── projectB
├── Deleted
├── Inbox
├── Junk
├── Sent
└── Tasks


 >
 >> 
 >> I get this error message from apple mail when I right click and 
choose 
 >> archive
 >> "The IMAP command "UID COPY" (to Archive) failed for the mailbox 
"INBOX" 
 >> with server error: Mailbox isn't selectable"
 >> 
 >
 >Did you notice that you have a mailbox called 'Archive' and namespace 
called
 >'Archive'? Namespace roots are not selectable, and this looks more 
like a 
 >config error.
 >
 >

That is been done on the advice I got here. 
Since November I am trying to get resolved, that I need my Archive and 
subfolders on different storage location as the default. Furthermore 
Archive folder is being used by apple mail, Archives folder eg. by 
Thunderbird. So it would be nice to 'group' this, so Thunderbird is not 
accidentally storing this on the default storage.

If the aliases plugin was working properly, I could have done this maybe 

via aliases
https://www.mail-archive.com/dovecot@dovecot.org/msg75587.html