I'm posting a method that may work providing nothing else you've done conflicts and it applies if you have a default Lubuntu 13.04 with Openbox managing your windows. Also, please read How do I open specific applications on specific workspaces in Lubuntu 13.04 in which I've covered other essential aspects (and omitted here).
In brief, you need to create a subsection in the
applications section of
~/.config/openbox/lubuntu-rc.xml for Thunderbird. The subsection would look like this:
<application name="..." class="...">
I'm purposely not being specific about
... because I don't have Thunderbird installed. But, you should be able to figure out what has to be inserted in place of both occurrences of
... after you read about
xprop in the linked answer. If the solution works for you, could you please come back and post the exact contents you use?
Here is code that makes
Firefox open "iconic" which is the term
Openbox uses to describe apps in a minimized state:
<application name="gedit" class="Gedit">
<application name="Navigator" class="Firefox">
If you're interested in using
lubuntu-rc.xml further, also look at Launching Windows Maximized and the section that follows.
Caveat: this procedure may not work for everything! I couldn't get
Transmission to open iconified with this code:
<application type="*" name="transmission-gtk" class="Transmission-gtk">