ThunderbirdCOMPOSE --> Shell
"C:\PortableSoftware\Seamonkey\App\SeaMonkey\seamonkey.exe" -osint -compose "%1"

ThunderbirdEML --> Shell --> open --> command
"C:\PortableSoftware\Seamonkey\App\SeaMonkey\seamonkey.exe" "%1"

ThunderbirdCOMPOSE --> Shell --> open --> command
"C:\PortableSoftware\Seamonkey\App\SeaMonkey\seamonkey.exe" -osint -compose "%1"

Clients -->  Mail --> Thunderbird --> shell --> open --> command
"C:\PortableSoftware\Seamonkey\App\SeaMonkey\seamonkey.exe" -mail

Clients\ -->  Mail --> Thunderbird --> shell --> properties --> command --> (Standard):
"C:\PortableSoftware\Seamonkey\App\SeaMonkey\seamonkey.exe" -options

Und sogar Safemode ist enthalten:
"C:\PortableSoftware\Seamonkey\App\SeaMonkey\seamonkey.exe" -safe-mode