Character not allowed in mailbox name: '.'

I’m starting to transfer mail from an Ubuntu server running Zimbra to a new Debian server running Hestia and I’ve run into Dovecot’s dreaded “Character not allowed in mailbox name: ‘.’” error. Oddly, when I tried transferring this same email directories to a Debian server running ISPConfig, Dovecot had no problem with the “.” in a folder name, despite the fact that ISPConfig left Dovecot’s default config of using a “.” as the mailbox separator character :face_with_raised_eyebrow:
I’m digging through the Dovecot settings of the server with ISPConfig and comparing them to this new server with Hestia to see if I can figure out why it works in the former and not the latter. But I wanted to see if anyone else has had this problem and already knows a solution.

Alright, I figured out why the folders with periods in them had transferred to the ISPConfig server without giving the error: the periods were automatically converted to underscores! I haven’t dug further to find out what was actually replacing those, but I suspect the imapsync script automatically did that due to the fact that ISPConfig had Dovecot configured to use “.” as the IMAP mailbox separator character. imapsync must have a routine in there to change any “.” to “" if the destination IMAP server has separator="." set. And since Hestia has separator set to “/”, imapsync didn’t bother to try to change the “.” to "”. So at least that mystery is solved.

That does leave, however, the fact that periods are still not allowed in folder names despite the fact that separator="/" is set in Dovecot. From what I’ve read, the underlying culprit is the Maildir++ format that all the mail is saved in. Its default setting—regardless of what Dovecot’s separator option is set to—is to create folders in the filesystem with IMAP mailbox names separated by a period. So rather than having separate directories, as such:


it stores all mailboxes in the same directory level, with submailboxes as separate directories in the same level, as such:


That behavior, however, can be changed by adding “LAYOUT=fs” to the mail_location option in 10-mail.conf. So, it would be something like this:

mail_location = maildir:%h/mail/%d/%n:LAYOUT=fs

Has anyone tried this when setting up a new Hestia installation? It would have to be added before any mail users had been created, because once you create one, it automatically creates “.Archive”, “.Drafts”, etc.

and where it states:
“Maildir++ layout disallows using the ‘.’ character (unless LAYOUT=fs is used), since it’s used internally as the folder hierarchy separator.”

Nice debug work you did here :slight_smile:.

Currently not, I didnt tried to adjust the maildir, because I’m happy with the current build. You can try to adjust the mail_location after a fresh install, basicly this should work and also it shouldnt get touched again during a hestia upgrade.

As it happens, yesterday I went ahead and deleted all the users from the new Hestia installation and spent most of the day experimenting with this. By late last night I finally got it all working beautifully. I can create mail folders with both periods and slashes in the names.

First, I’ll show all the modifications I made to various config files, then I’ll give a full explanation, then show the results…


In /etc/dovecot/dovecot.conf, added the following lines at the top, just before the !include lines:

log_timestamp = "%Y-%m-%d %H:%M:%S "
mail_plugins = listescape

and changed separator in the namespace to a tilde:

separator = "~"

In /etc/dovecot/conf.d/20-imap.conf, changed the mail_plugins line to read as follows (so that it would include the “listescape” from dovecot.conf):

mail_plugins = $mail_plugins quota imap_quota

In /etc/dovecot/conf.d/10-mail.conf, changed mail_location to the following:

mail_location = maildir:%h/mail/%d/%n/store:LAYOUT=fs:FULLDIRNAME=0_FolderContent:UTF-8:INDEX=%h/mail/%d/%n/index:CONTROL=%h/mail/%d/%n/control:VOLATILEDIR=%h/mail/%d/%n/volatile

In /etc/exim4/exim4.conf.template:
under “local_delivery” transport, changed directory to the following, and copied the “quota_directory” line from local_spam_delivery:

directory = "${extract{5}{:}{${lookup{$local_part}lsearch{/etc/exim4/domains/$domain/passwd}}}}/mail/$domain/$local_part/store/INBOX/0_FolderContent"
quota_directory = "${extract{5}{:}{${lookup{$local_part}lsearch{/etc/exim4/domains/$domain/passwd}}}}/mail/$domain/$local_part"

under “local_spam_delivery” transport, changed directory to the following:

directory = "${extract{5}{:}{${lookup{$local_part}lsearch{/etc/exim4/domains/$domain/passwd}}}}/mail/$domain/$local_part/store/Junk/0_FolderContent"


Problem 1: Periods in Folder Names – As I said in the previous post, Dovecot’s default Maildir format is “LAYOUT=Maildir++”, which stores all mail subfolders as single filesystem directories named with the full path of the mail subfolders (with names separated by periods). So for example, if you had a “Correspondence” mail folder with a “Work” subfolder and subfolders with people’s names within that, they would be stored as follows:


Consequently, the user cannot create mail folders containing periods, as they often would when they want to have a typical abbreviation in the name. So a folder like the following would not be allowed: “/home/user/mail/domain/user/.Correspondence.Work.Mr. Rogers/”. If, however, you specify “LAYOUT=fs” for the Maildir format in Dovecot’s mail_location directive, it will store each mail folder as a regular directory in the filesystem. That alleviates the restriction on periods, so “/home/user/mail/domain/user/Correspondence/Work/Mr. Rogers/” will work fine. Now the above example will be stored as follows:

/home/user/mail/domain/user/Correspondence/Work/Mr.\ Rogers/

Problem 2: Slashes in Folder Names – Let’s face it, the slash is a commonly used punctuation mark: he/she, 2018/2019, this/that. It’s kind of absurd that in the year 2020 people still can’t use slashes in mail folder names. Luckily, Dovecot has a solution for that. First, enable the “listescape” plugin that comes with Dovecot, which “escapes” special characters in filesystem directory names. Second, change the mail folder separator to something far less common, such as a backslash or tilde. I chose tilde because I’ve read that backslash sometimes causes problems.

Problem 3: Folder Name Conflicts – When all the metadata files are stored in the same directories as the actual mail folders and messages—and hidden from view by Dovecot—the potential is always there that a user may try to create a folder with the same name as one of the hidden files/directories. Luckily, Dovecot offers several ways to deal with that:

First, In every mail folder, Dovecot creates three subfolders for its own internal use: cur, new, tmp. Both “new” and “tmp” could conceivably be problematic. In the mail_location directive, you can use the FULLDIRNAME option to tell Dovecot to put those three directories into a single directory with a name that no one would most likely try to use as their own subfolder name. The Dovecot documentation gives an example of “mAildir”. Meh, that seems odd. I’d rather name it something meaningful, like “FolderContent”. And I added “0_” to the beginning of it so that (1) it would always be output at the top of the directory list and (2) to make it far less likely that anyone would try to create their own mail folder by that name. One side effect of using the FULLDIRNAME option is that, rather than creating a “0_FolderContent” directory at the root of the tree, Dovecot instead creates a directory named “INBOX” with its own 0_FolderContent directory. That’s why I had to add that to the “directory” lines in exim4.conf.template.

Second, Dovecot allows you to make a clean separation between the locations where it stores the actual mailbox data, the indexes, and other “control” files that Dovecot uses. These locations are specified in the mail_location directive in /etc/dovecot/conf.d/10-mail.conf with options named INDEX, CONTROL, and VOLATILEDIR. Doing this has several advantages: (1) the directory storing the actual email messages doesn’t have extraneous, “hidden” files in it that aren’t part of the user’s mail content; (2) you have the option of putting the indexes on fast SSD storage (or even a ramdisk, I suppose); (3) the base directory is then left open for other config files, such as sieve filters, rather than putting them as hidden files in the directory where the mail folders are actually stored. So with this new config, a user’s mail directory contains the following four directories: control, index, store, volatile. I’m going to be experimenting with getting sieve to work with RoundCube, so this will allow me to add a “sieve” directory alongside these others.

And a few final side notes:
I just added log_timestamp = "%Y-%m-%d %H:%M:%S " because I hate it when log file times aren’t in ISO format :-).
And in dovecot.conf, I changed mailbox Junk to auto=subscribe and set mailbox Spam to auto=no, just because in my experience, “Junk” is the most common, standard, default name for the junk folder in email clients.


SO, I’ve created a “test” user to try these things out. Here’s what the directories look like for that user:

$ ll /home/example/mail/
drwx------ 8 example mail 188 2020-03-23 12:50:17 control/
drwx------ 8 example mail 142 2020-03-23 12:49:45 index/
drwx------ 8 example mail  85 2020-03-23 12:49:45 store/
drwx------ 2 example mail   6 2020-03-23 12:50:17 volatile/

$ ll /home/example/mail/
drwx------ 4 example mail 48 2020-03-23 12:50:17 Archive/
drwx------ 3 example mail 29 2020-03-23 12:49:45 Drafts/
drwx------ 3 example mail 29 2020-03-23 12:46:35 INBOX/
drwx------ 3 example mail 29 2020-03-23 12:49:45 Junk/
drwx------ 3 example mail 29 2020-03-23 12:49:45 Sent/
drwx------ 3 example mail 29 2020-03-23 12:49:45 Trash/

$ ll /home/example/mail/
drwx------ 2 example mail 60 2020-03-23 12:49:45 cur/
-rw-rw---- 1 example mail 17 2020-03-23 12:48:42 maildirsize
drwx------ 2 example mail  6 2020-03-23 12:49:45 new/
drwx------ 2 example mail  6 2020-03-23 12:48:42 tmp/

In RoundCube, I created a folder named “2017/2018” in the Archive folder. Thanks to the Dovecot “listescape” plugin, here’s how it created the actual filesystem directory:

$ ll /home/example/mail/
drwx------ 5 example mail 39 2020-03-23 12:49:45  0_FolderContent/
drwx------ 3 example mail 29 2020-03-23 12:50:17 '2017\2f2018'/
drwx------ 3 example mail 29 2020-03-23 13:37:28 'Lou. Area Humanists'/

And here are the metadata directories:

$ ll /home/example/mail/
drwx------ 4 example mail 48 2020-03-23 12:50:17 Archive/
-rw------- 1 example mail  8 2020-03-23 12:50:17 dovecot-uidvalidity
-r--r--r-- 1 example mail  0 2020-03-23 12:46:35 dovecot-uidvalidity.5e78f601
drwx------ 3 example mail 29 2020-03-23 12:49:45 Drafts/
drwx------ 3 example mail 29 2020-03-23 12:46:35 INBOX/
drwx------ 3 example mail 29 2020-03-23 12:49:45 Junk/
-rw------- 1 example mail 10 2020-03-23 12:49:44 maildirsize
drwx------ 3 example mail 29 2020-03-23 12:49:45 Sent/
-rw------- 1 example mail 56 2020-03-23 12:50:17 subscriptions
drwx------ 3 example mail 29 2020-03-23 12:49:45 Trash/

$ ll /home/example/mail/
drwx------ 4 example mail   48 2020-03-23 12:50:17 Archive/
-rw------- 1 example mail 3.8K 2020-03-23 12:50:17 dovecot.list.index.log
-rw------- 1 example mail  144 2020-03-23 12:50:17 dovecot.mailbox.log
drwx------ 3 example mail   29 2020-03-23 12:49:45 Drafts/
drwx------ 3 example mail   29 2020-03-23 12:46:35 INBOX/
drwx------ 3 example mail   29 2020-03-23 12:49:45 Junk/
drwx------ 3 example mail   29 2020-03-23 12:49:45 Sent/
drwx------ 3 example mail   29 2020-03-23 12:49:45 Trash/

All of the mail from the Zimbra server is currently being transferred and hasn’t run into any problems.

For the sake of completeness, if anyone is interested, here’s the imapsync command I’m using to transfer a user account. I’ve used this many times over the past 20 years or so to transfer back and forth between old Linux servers with everything in mbox files, Cyrus servers, Exchange, Zimbra, ISPConfig, and now this.

mkdir /var/tmp/imapsync
imapsync --host1 SOURCEIPADDRESS --port1 993 --ssl1 --user1 USERNAME --password1 'PASSWORD' \
    --host2 localhost --port2 993 --ssl2 --user2 'USERNAME' --password2 'PASSWORD' \
    --nofoldersizes --nofoldersizesatend --skipsize --nocheckmessageexists \
     --delete2 --useuid --tmpdir /var/tmp/imapsync

Make sure you have enough space on the drive where you put the tmpdir. It will create a cache directory so that you can keep re-syncing and it won’t have to resync everything all over again, only the changes.

Hope everyone’s staying safe.

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Shazam!!! One of the larger email user mailboxes (about 6 gig) just got finished syncing from Zimbra to the Hestia server without error.

imapsync results:

Transfer started on                     : Mon Mar 23 16:08:36 2020
Transfer ended on                       : Mon Mar 23 17:09:28 2020
Transfer time                           : 3652.3 sec
Folders synced                          : 239/239 synced
Messages transferred                    : 114240 
Messages skipped                        : 0
Messages found duplicate on host1       : 0
Messages found duplicate on host2       : 0
Messages found crossduplicate on host2  : 0
Messages void (noheader) on host1       : 0  
Messages void (noheader) on host2       : 0
Messages found in host1 not in host2    : 0 messages
Messages found in host2 not in host1    : 0 messages
Messages deleted on host1               : 0
Messages deleted on host2               : 0
Total bytes transferred                 : 6211546435 (5.785 GiB)
Total bytes skipped                     : 0 (0.000 KiB)
Message rate                            : 31.3 messages/s
Average bandwidth rate                  : 1660.9 KiB/s
Reconnections to host1                  : 0
Reconnections to host2                  : 0
Memory consumption at the end           : 310.0 MiB (started with 162.0 MiB)
Load end is                             : 0.88 0.86 0.80 1/281 on 2 cores
Biggest message                         : 77507108 bytes (73.917 MiB)
Memory/biggest message ratio            : 4.2
The sync is strict,  all 0 identified messages in host2 are on host1.
Detected 0 errors
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Congratulation! Thanks that you share your knowledge, this will help other users if they have to do the same steps.