Is it possible to add into t he toolbar a pushbutton that, when clicked, opens up a mail window? I know that it's possible with an  "image" (Tips&Tricks Nr. 22), but we would prefer a toolbar button.

You can put the image into the toolbar with 

Image (toolbar) .....   start=....

Or you use a pushbutton and the "Start" command in an InputScript:

Pushbutton (toolbar) "Send email"  process="mail.txt"

// InputScript  "mail.txt"

start "mailto:service@abcd.com?subject=Logon in system&V[_database]&body=Hello"

Return

(supported with GuiXT 2007 Q4 5 and upwards)