Actually, I think only Mailing Online is Tcl. See COMPANY: BAE Systems, Business Systems Group (BSG).
Mailing Online (MOL) is one component of the USPS NetPost program. 99% of MOL is TCL - this includes the web server AOLserver, the backend processing, and the print site formating and control. The other 1% is VB ( :-( used to control some MS apps ) and 'C' wrappers to third party packages.
I know this info to be accurate - I [L3 ] designed the systems and wrote a large portion of it for BAE Systems.
TclMML is a Tcl package to interface with Mailing Online via the Mail Management Language (XML dialect).