"Other systems produce [FTN MSG-IDs for NetMail messages) quite nicely: HotdogEd, BBBS, Mageia, Platinum
Express, GED+LNX, and OpenXP.   I took it for granted that SBBS would be
in the same league.   It makes it super easy to link up a netmail
conversation or generate a graphical-tree when a msgid exists.

I was spoiled into thinking that msgid was ubiquitous in netmail as well."

Reviewing FTS-9, I see no restriction to only echomail, so sure, why not:
add_msg_ids() now adds FTN Message-IDs to outbound NetMail messages too (not just FTN echomail). No configuration or SBBSecho change needed.