Character not allowed in mailbox name

Arnold Opio Oree arnoldoree at
Mon Jul 22 11:49:37 EEST 2019

Hi Lothar,

I haven't yet had the opportunity to go deep into Dovecot engineering /
development, (so please correct me if necessary anyone).

I have experienced this exception where attempting to copy mailbox data
within a client from IMAP account to IMAP account, but I have not had
it cause a mailbox to become inaccessible.

The reason was because Maildir++ format uses the "." separator to
delineate child directories, and therefore the character is illegal in
mailbox names. The issue was addressed by either changing the
filesystem layout to LAYOUT=fs or by changing the mailbox format
altogether to e.g. sdbox.

>   location = maildir:%%h:INDEX=%h/shared/%%u

I can see from your configuration that the LAYOUT is not set as fs, so
I would assume is still using Maildir++.

Perhaps this setting was lost during the upgrade?


Arnold Opio Oree
Chief Executive Officer
Parallax Digital Technologies

arnoldoree at

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-----Original Message-----
From: Lothar Schilling via dovecot <dovecot at>
Reply-To: Lothar Schilling <ls at>
To: dovecot at
Subject: Character not allowed in mailbox name
Date: Mon, 22 Jul 2019 08:33:45 +0200

Hi everybody,

after an update this morning to dovecot 2.3.7 we cannot connect to our
shared mailboxes anymore. The error message as issued in Thunderbird:

"Character not allowed in mailbox name '.'"

I didn't change anything about the configuration. Output of dovecot -n:

namespace {
  list = children
  location = maildir:%%h:INDEX=%h/shared/%%u
  prefix = Shared/%%u/
  separator = /
  subscriptions = yes
  type = shared

Any help would be appreciated, thank you very much.

Lothar Schilling

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