Can I get a notification when an email arrives in a sub folder?
There are many email apps for Android, each one should have an option within the app itself where you can check or uncheck to be notified of a new email arrival.
This list covers the most popular ones:
Email
Allows you to have a notification on the status bar, when activated within the application:

Access the application;
Tap your device &quot;home&quot; button;
Tap &quot;Account Settings&quot;;
Scroll your way to &quot;Notification settings&quot;;
Tick the checkbox for &quot;Email notifications&quot;.

Gmail
Allows you to have a notification on the status bar for each one of the configured accounts. Can be activated within the application:

Access the application;
Tap your device &quot;home&quot; button;
Tap &quot;more&quot;;
Tap &quot;Settings&quot;;
Tap over the desired account;
Scroll your way to &quot;Notification settings&quot;;
Tick the checkbox for &quot;Email notifications&quot;.

K-9 Mail
Allows you to have a notification on the status bar for each one of the configured accounts. Can be activated within the application:

Access the application;
Tap your device &quot;home&quot; button;
Tap &quot;more&quot;;
Tap &quot;Accounts&quot;;
Long Tap over the desired account;
From the popup, tap &quot;Account settings&quot;;
Scroll your way to &quot;Notifications&quot; and tap it;
Tick the checkbox for &quot;New mail notifications&quot;.

MailDroid
Allows you to have a notification on the status bar, when activated within the application:

Access the application;
Tap your device &quot;home&quot; button;
Tap &quot;Preferences&quot;;
Scroll your way to &quot;Notifications&quot; and tap it;
Select the icon for the status bar from the dropdown;
Tick the checkbox for &quot;Show separate notification&quot;, aditionally you can tick the checkbox for &quot;show once&quot;;

Yahoo! Mail
Allows you to have a notification on the status bar for each one of the configured accounts. Can be activated within the application:

Access the application;
Tap your device &quot;home&quot; button;
Tap &quot;Options&quot;;
Tap the desirable account;
Tap &quot;Notification Settings&quot;;
Tick the checkbox for &quot;Show in Status Bar&quot;.

Hotmail
Allows you to have a notification on the status bar, when activated within the application:

Access the application;
Tap your device &quot;home&quot; button;
Tap &quot;Account Settings&quot;;
Scroll your way to &quot;General Settings&quot; and tap it;
Scroll your way to &quot;Notifications and Alerts&quot; and tap it;
Tap &quot;Email Notifications&quot;;
Tick the checkbox for &quot;Message Notification&quot;.


Notes:

Some Email apps, in order to notify you of the arrival of new mail, need to have the &quot;auto-sync&quot; and the &quot;Background Data&quot; active on your phone settings:
This options are found on your device settings, under &quot;Accounts &amp; sync&quot;.

&quot;Tick the checkbox&quot; stands for having the checkbox with a green tick on it. The gray tick is the disable status.

If your email app isn't present on the above list, feel free to @Zuul me and I'll be glad to add it to the list.

Only email app with Notification capabilities will be present.