Add documentaiton for mail app

Signed-off-by: greta <gretadoci@gmail.com>

user_manual/groupware/index.rst

@@ -16,6 +16,7 @@ You can find out more about Nextcloud Groupware `on our website <https://nextclo
 
    contacts
    calendar
+   mail
    sync_android
    sync_ios
    sync_osx

user_manual/groupware/mail.rst

@@ -0,0 +1,93 @@
+===================
+Using the Mail app
+===================
+
+.. note:: The Mail app comes installed with Nextcloud Hub by default, but can be disabled.
+          Please ask your Administrator for it.
+
+.. figure:: images/mail.png
+
+Managing your mail account
+---------------------------
+
+Add a new mail account
+~~~~~~~~~~~~~~~~~~~~~~~
+
+1. Enable mail app from the apps
+2. Click the mail icon on the header
+3. Fill up the login form (auto or manual)
+
+.. figure:: images/new-mail-account.png
+
+
+Create/Write a new message
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+1. Click new message on the top left of your screen
+2. Start writing your message
+
+Scheduled messages
+~~~~~~~~~~~~~~~~~~~
+1. Click new message button on top left of your screen
+2. Click the (...) action menu on the modal composer
+3. Click *send later*
+
+.. figure:: images/scheduled-msg.png
+
+Priority inbox
+~~~~~~~~~~~~~~~
+Priority inbox has 2 section *Important* and *Others*.
+Messages will automatically be marked as important based on which messages you interacted with or marked as important. In the beginning you might have to manually change the importance to teach the system, but it will improve over time.
+
+.. figure:: images/priority-inbox.png
+
+All inboxes
+~~~~~~~~~~~~
+All messages from all the accounts you have logged in, will be shown here chronologically.
+
+Account settings
+~~~~~~~~~~~~~~~~~
+Your account settings such as:
+
+1. Aliases
+2. Signature
+3. Default Folders
+4. Autoresponder
+5. Trusted server ect
+
+Can be found in the action menu of a mail account. There you can edit, add or remove settings depending on your need.
+
+Mailbox actions
+---------------
+
+Add a mailbox
+~~~~~~~~~~~~~~
+1. Open the action menu of an account
+2. Click add mailbox
+
+Add a submailbox
+~~~~~~~~~~~~~~~~~
+1. Open the action menu of a mailbox
+2. Click add submailbox
+
+Shared mailbox
+~~~~~~~~~~~~~~~
+If a mailbox was shared with you with some specific rights, that mailbox will show as a new mailbox with a shared icon as below:
+
+.. figure:: images/shared-mailbox-icon.png
+
+Envelope actions
+----------------
+
+Create an event
+~~~~~~~~~~~~~~~~
+Create an event for a certain message/thread directly via mail app
+1. Open action menu of an envelope
+2. Click *more actions*
+3. Click *create event*
+
+Edit tags
+~~~~~~~~~~
+1. Open action menu of an envelope
+2. Click *Edit tags*
+3. On the tags modal, set/unset tags