(In reply to comment #0)
> However, I have not found anywhere in the documentation or configuration
> windows a way to make the program NOT START minimized.
> 
Have you installed and activated the notification plugin?
If so:
1) Configuration->Preferences...->Plugins->Notification->SysTrayicon
2) Uncheck second check button "Hide at start-up"

or the Trayicon plugin which also provides this functionality.

I don't have neither of those plugins installed... the only plugins that my
claws-mail installation has loaded are: AttRemover, PGP/Core, PGP/MIME, and the
HTML GTK visualizer.

Even after unloading all modules the "problem" persists... Perhaps it is a
problem with an old ~/.claws-mail configuration directory? Nope, even moving
.claws-mail to another location and starting a fresh installation exhibits this
problem.

So this isn't then the normal program behaviour...?

what window manager do you use?

I use PekWM. I switched to Fluxbox (my previous window manager) to test things
out, and Claws-Mail did not start iconified. However this doesn't mean that the
bug is in PekWM, because xprop again displays:

WM_HINTS(WM_HINTS):
        Client accepts input or input focus: True
        Initial state is Iconic State.
        bitmap id # to use for icon: 0x1c00037
        bitmap id # of mask for icon: 0x1c00039
        window id # of group leader: 0x1c00001


So PekWM is simply doing what the WM_HINTS say it should be doing (and for some
reason Fluxbox is not respecting that). Or does Claws-Mail in general expects
that initial state hint to not be respected?

Claws Mail starts iconified and de-iconifies according to user's preferences.
gtk_window_deiconify() is used for that. 

xprop says:
        window state: Normal
                [...]
        Initial state is Iconic State.

I think "Initial state" should not be "one and only state" and the bug is in
PekWM.

Confirmed, thanks for the head-up, now I see what is going on.

Even though it seems (to me) a bit strange to start iconified and then
de-iconify rather than simply not displaying the window until the contents are
ready...

The code for 3.7.0 uses no pref, it simply deiconifies on the first call to
main_window_popup.

void main_window_popup(MainWindow *mainwin)
{
   static gboolean first_start = TRUE;

   if (!GTK_WIDGET_VISIBLE(GTK_WIDGET(mainwin->window)))
      main_window_show(mainwin);

   if (prefs_common.mainwin_maximised)
      gtk_window_maximize(GTK_WINDOW(mainwin->window));

   if (first_start) {
      gtk_window_deiconify(GTK_WINDOW(mainwin->window));
      first_start = FALSE;
   } ...