14.2. Management of the mail server data

14.2.1. Management of mail domains

A mail domain is an common namespace for email addresses, mailing lists and IMAP group folders. Postfix differentiates between the delivery of emails between local and external domains. Delivery to mailboxes defined in the LDAP directory is only conducted for email address from local domains. The name of a mail domain may only be composed of lowercase letters, the figures 0-9, full stops and hyphens.

Several mail domains can be managed with UCS. The managed mail domains do not need to be the DNS domains of the server - they can be selected at will. The mail domains registered on a mail server are automatically saved in the Univention Configuration Registry Variable mail/hosteddomains.

To ensure that external senders can also send emails to members of the domain, MX records must be created in the configuration of the authoritative name servers, which designate the UCS server as mail server for the domain. These DNS adjustments are generally performed by an internet provider.

Mail domains are managed in the UMC module Mail with the Mail domain object type.

14.2.2. Assignment of email addresses to users

A user can be assigned three different types of email addresses:

Primary email address

The primary email address is used for authentication on Postfix and Dovecot. Primary email addresses must always be unique. Only one primary email address can be configured for every user. It also defines the user’s IMAP mailbox. If a mail home server is assigned to a user (see Distribution of an installation on several mail servers), the IMAP inbox is automatically created by a Univention Directory Listener module. The domain part of the email address must be registered in the UMC module Mail (see Management of mail domains).

Alternative email addresses

Emails to alternative email addresses are also delivered to the user’s mailbox. As many addresses can be entered as you wish. The alternative email addresses do not have to be unique: if two users have the same email address, they both receive all the emails which are sent to this address. The domain part of the email address must be registered in the UMC module Mail (see Management of mail domains). To receive emails to alternative email addresses, a user must have a primary email address.

Note

When setting the Univention Configuration Registry Variable directory/manager/mail-address/uniqueness to true the Alternative email addresses must be unique across the domain. No other user can have the same alternative address assigned.

Forward email addresses

If forward email addresses are configured for a user, emails received through the primary or alternative email addresses are forwarded to them. A copy of the messages can optionally be stored in the user’s mailbox. Forward email addresses do not have to be unique and their domain part does not have to be registered via a UMC module.

Note

Email addresses can consist of the following characters: letters a-z, figures 0-9, dots (.), hyphens (-) and underscores (_). The address has to begin with a letter and must include an @ character. At least one mail domain must be registered for to be able to assign email addresses (see Management of mail domains).

Email addresses are managed in the UMC module Users. The primary email address is entered in the General tab in the User account submenu. Alternative email addresses can be entered under Advanced settings ‣ Mail.

Note

Once the user account is properly configured, authentication to the mail stack is possible (IMAP/POP3/SMTP). Please keep in mind that after disabling the account or changing the password, the login to the mail stack is still possible for 5 minutes due to the authentication cache of the mail stack. To invalidate the authentication cache run

$ doveadm auth cache flush

on the mail server. The expiration time of the authentication cache can be configured on the mail server with the Univention Configuration Registry Variable mail/dovecot/auth/cache_ttl and mail/dovecot/auth/cache_negative_ttl.

14.2.3. Management of mailing lists

Mailing lists are used to exchange emails in closed groups. Each mailing list has its own email address. If an email is sent to this address, it is received by all the members of the mailing list.

Fig. 14.1 Creating a mailing list

Mail domains are managed in the UMC module Mail with the Mailing list object type. A name of your choice can be entered for the mailing list under Name; the entry of a Description is optional. The email address of the mailing list should be entered as the Mail address. The domain part of the address needs to be the same as one of the managed mail domains. As many addresses as necessary can be entered under Members. In contrast to mail groups (see Management of mail groups), external email addresses can also be added here. The mailing list is available immediately after its creation.

By default everyone can write to the mailing list. To prevent misuse, there is the possibility of restricting the circle of people who can send mails. To do so, the Univention Configuration Registry Variable mail/postfix/policy/listfilter on the mail server must be set to yes and Postfix restarted. Users that are allowed to send emails to the list and Groups that are allowed to send emails to the list can be specified under Advanced settings. If a field is set here, only authorized users/groups are allowed to send mails.

14.2.4. Management of mail groups

There is the possibility of creating a mail group: This is where an email address is assigned to a group of users. Emails to this address are delivered to the primary email address of each of the group members.

Mail groups are managed in the UMC module Groups (see Group management).

The email address of the mail group is specified in the mail address input field under Advanced settings. The domain part of the address must be the same as one of the managed mail domains.

By default everyone can write to the mail group. To prevent misuse, there is the possibility of restricting the circle of people who can send mails. To do so, the Univention Configuration Registry Variable mail/postfix/policy/listfilter on the mail server must be set to yes and Postfix restarted.

Users that are allowed to send emails to the group and Groups that are allowed to send emails to the group can be specified under Advanced settings. If a field is set here, only authorized users/groups are allowed to send mails.

14.2.5. Management of shared IMAP folders

Shared email access forms the basis for cooperation in many work groups. In UCS, users can create folders in their own mailboxes and assign permissions so that other users may read emails in these folders or save additional emails in them.

Alternatively, individual IMAP folders can be shared for users or user groups. This type of folder is described as a shared IMAP folder. Shared IMAP folders are managed in the UMC module Mail with the Mail folder (IMAP) object type.

Shared folders cannot be renamed, therefore the Univention Configuration Registry Variable mail/dovecot/mailbox/rename is not taken into account. When a shared folder is deleted in the UMC module Mail, it is only deleted from the hard disk, if mail/dovecot/mailbox/delete is set to yes. The default value is no.

Fig. 14.2 Creating a shared IMAP folder

14.2.5.1. Shared IMAP folder - General tab

Table 14.1 General tab

Attribute	Description
Name (*)	The name under which the IMAP folder is available in the email clients. The name displayed in the IMAP client differs depending on if an email address is configured (see field Email address) or not. If no email address is configured, the IMAP folder will be displayed in the client as name@domain/INBOX. If an email address is configured, it will be shared/name@domain.
Mail domain (*)	Every shared IMAP folder is assigned to a mail domain. The management of the domains is documented in the Management of mail domains.
Mail home server (*)	An IMAP folder is assigned to a mail home server. Further information can be found in Distribution of an installation on several mail servers.
Quota in MB	This setting can be used to set the maximum total size of all emails in this folder.
Email address	An email address can be entered here via which emails can be sent directly to the IMAP folder. If no address is set here, it is only possible to write in the folder from email clients. The domain part of the email address must be registered in the UMC module Mail (see Management of mail domains).

14.2.5.2. Shared IMAP folder - Access rights tab

Table 14.2 Access rights tab

Attribute

Description

Name (*)

Access permissions based on users or groups can be entered here. Users are entered with their username; the groups saved in the UMC module Groups can be used as groups. The access permissions have the following consequences for individual users or members of the specified group: No access No access is possible. The folder is not displayed in the folder list. Read The user may only perform read access to existing entries. Append Existing entries may not be edited; only new entries may be created. Write New entries may be created in this directory; existing entries may be edited or deleted. Post Sending an email to this directory as a recipient is permitted. This function is not supported by all the clients. All Encompasses all permissions of write and also allows the changing of access permissions.

14.2.6. Mail quota

The size of the users’ mailboxes can be restricted via the mail quota. When this is attained, no further emails can be accepted for the mailbox by the mail server until the user deletes old mails from their account.

The limit is specified in megabytes in the Mail quota field under Advanced settings ‣ Mail. The default value is 0 and means that no limit is set. The multi edit mode of UMC modules can be used to assign a quota to multiple users at one time, see Editing objects.

The user can be warned once a specified portion of the mailbox is attained and then receives a message that their available storage space is almost full. The administrator can enter the threshold in percent and the messages subject and text:

• The threshold for when the warning message should be issued can be configured in the Univention Configuration Registry Variable mail/dovecot/quota/warning/text, for example mail/dovecot/quota/warning/text/PERCENT=TEXT

  PERCENT must be a number between 0 and 100 without the percent sign.

  TEXT will be the content of the email. If the value TEXT contains the string $PERCENT, it will be replaced in the email with the value of the limit that has been exceeded.

  The value of the Univention Configuration Registry Variable mail/dovecot/quota/warning/subject will be used for the subject of the email.

• When the mail server package is installed, a subject and two warning messages are automatically configured:

  • mail/dovecot/quota/warning/subject is set to Quota-Warning

  • mail/dovecot/quota/warning/text/80 is set to Your mailbox has filled up to over $PERCENT%.

  • mail/dovecot/quota/warning/text/95 is set to Attention: Your mailbox has already filled up to over $PERCENT%. Please delete some messages or contact the administrator.