VMM/cli: Activated help subcommand.
Implemented Command.help_(), which reads the command's help message from
cli.clihelp.
========================
Managing alias addresses
========================
aliasadd
--------
Syntax:
| **vmm aliasadd** *address destination ...*
| **vmm aa** *address destination ...*
This subcommand is used to create a new alias *address* with one or more
*destination* addresses.
Within the destination address, the placeholders **%n**, **%d**, and **%=**
will be replaced by the local-part, the domain, or the email address with
**@** replaced by **=** respectively.
In combination with alias domains, this enables domain-specific destinations.
Example:
.. code-block:: console
root@host:~# vmm aliasadd john.doe@example.com d.user@example.com
root@host:~# vmm aa support@example.com d.user@example.com e.user@example.com
root@host:~# vmm aa postmaster@example.com postmaster+%d@example.org
aliasdelete
-----------
Syntax:
| **vmm aliasdelete** *address* [*destination*]
| **vmm ad** *address* [*destination*]
Use this subcommand to delete the alias with the given *address*.
If the optional *destination* address is given, only this destination will
be removed from the alias.
Example:
.. code-block:: console
root@host:~# vmm ad support@example.com d.user@example.com
aliasinfo
---------
Syntax:
| **vmm aliasinfo** *address*
| **vmm ai** *address*
Information about the alias with the given *address* can be displayed with
this subcommand.
Example:
.. code-block:: console
root@host:~# vmm aliasinfo support@example.com
Alias information
-----------------
Mail for support@example.com will be redirected to:
* e.user@example.com