Thanks for reply, I really appreciate it - Yes, I understand all that and also don't get it. There is no typo or anything in dovecot.conf or any other configuration file. The thing is that when I enable Sieve in sogo.conf (the file that comes with iRedmail setup), it creates another maildir folder, as I am in a Linux OS., uppercase and lowercase are sensitive, resulting in two folders.

Here are the segments that has something to do with maildir folder creation in my /etc/dovecot/dovecot.conf:

mail_location = maildir:%Lh/Maildir/:INDEX=%Lh/Maildir/
    location = maildir:/var/vmail/vmail1/%Ld/%%Ln/Maildir/:INDEXPVT=/var/vmail/vmail1/%Ld/%%Ln/Maildir/Shared/%%u

A here is the only segment that has something to do with maildir folder creation in my /etc/dovecot/dovecot-ldap.conf:

user_attrs      = =home=/var/vmail/vmail1/%Ld/%Ln/Maildir/,=mail=maildir:/var/vmail/vmail1/%Ld/%Ln/Maildir/,=quota_rule=*:storage=%{ldap:ipPhone}M

   Before asking for support here, I've spent the entire morning trying to find an answer.

Well, thank you for your time and help.

I could reproduce it with a new user. Here are the steps:

1 - Created a new AD user;
2 - SOGo, Login with the new user;
3 - Went to Preferences -> Mail -> Vacantion;
4 - Marked "Enable vacation auto reply";
5 - Went back to INBOX without saving.

Ended up with this:

Yes, there is a "sieve" folder, which contains an empty folder called "tmp".

It may not be a big deal if I can achieve what I am trying to do. I am trying to mount a NTFS sharing, and move the mail folders to this mounted driver. If I succeed, then it will not be a problem, because Windows isn't case sensitive, so folders "maildir" and "Maildir" will be the same.

Yesterday I was able to mount the driver and access my e-mails using SOGo and Outlook, I could send and receive e-mail and the new files were created in Windows share. But I couldn't share mail folders, like my Inbox, for example, it just didn't "remember" the sharing after logging out.

Another problem is that it is not mounting the driver automatically when booting the system, sometimes it hangs and sometimes it asks me to interact by pressing "s" or "m" to skip or manual recover.

So, if I make it work, then the duplicated folders will not be a problem for me anymore.

I'll let you know if I succeed or not.

I know this is an old topic but I have just faced this problem.

in /dovecot/dovecot.conf we had:
sieve_dir = %Lh/sieve
sieve = %Lh/sieve/dovecot.sieve

That %Lh was doing the mess, just leaving it like this:

sieve_dir = %h/sieve
sieve = %h/sieve/dovecot.sieve

made the trick.

I hope this help someone

The home folder (%h) is something like /var/xxxxx/user_name/Maildir
If we use %Lh it puts the string in lowercase so it's: /var/xxxxx/user_name/maildir and there is where the duplicated folder comes out.

In short:

%h = /user_name/Maildir
%Lh = /user_name/maildir

I'm trying to explain myself but English it's not my first language, sorry about that.

Yes, you're correct, %h is home dir not mail dir, sorry.

But the fact is that removing the %L did the trick for me (luckily :$).  I didn't find any config file where  I manually append "Maildir" so it can be some kind of bug, I'm not sure, I'll give it another try this evening and keep this updated.

UPDATE:

I think I've found it, I have this configuration line:
user_attrs      = =home=/var/vmail/vmail1/%Ld/%Ln/Maildir/,=mail=maildir:/var/vmail/vmail1/%Ld/%Ln/Maildir/

That makes "home" and "Maildir" the same so that's because that "L" created the /maildir,  am I right?

The value for user_attrs is from: https://docs.iredmail.org/active.directory.html