Mixed case group name prevents access to public Mail folder

[mrmarkuz]

If a group provided by any user domain contains a capital letter in the name like "Marketing" and it's assigned to a public mail folder, it's members don't get the permissions to access the public mail folder. I tested with SOGo, Roundcube and Webtop.
After removing and recreating the group as "marketing" (lower case) in Users and Groups page, the permissions are working again.

After setting permissions for the group with capital letter using doveadm, the user can see the public folder:

/var/lib/vmail # doveadm acl set -u markus Public/MarketingPF group=Marketing admin create delete expunge insert lookup post read write write-deleted write-seen
/var/lib/vmail # doveadm acl get -u markus Public/MarketingPF
ID              Global Rights                                                                                       
group=Marketing        admin create delete expunge insert lookup post read write write-deleted write-seen           
group=marketing        admin create delete expunge insert lookup post read write write-deleted write-seen

I think the group names are converted to lower case and therefore the dovecot ACL doesn't work, see https://github.com/search?q=org%3ANethServer%20group%20.lower&type=code

Steps to reproduce

• Create a user domain
• Add a user "user1"
• Add a group with capital letter like "Marketing"
• Add the user "user1"` to the group "Marketing"
• Install mail app
• Configure mail app
• Add a public mailbox "MarketingPF" and set the members to group "marketing"

Expected behavior

All members of the group "Marketing" should be able to access the public mailfolder "MarketingPF" in the mail clients like roundcube, sogo or webtop.

Actual behavior

The members of the group can't even see the public mailfolder "MarketingPF"

Components

• Core 3.8.0
• Mail 1.6.3

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Thanks to Harald

[DavidePrincipi]

In Testing mail 1.6.4-dev.1

Test case

Verify that the bug is not reproducible with the version from Testing.