https://gitlab.synchro.net/main/sbbs/-/merge_requests/245#note_3113
That seems to happen when someone using the guest account sends an email to the sysop. I've tried sending an email to me (the sysop) on my BBS from the guest account and have seen the message say it's from "All"
--- SBBSecho 3.20-Linux
* Origin: Vertrauen - [vert/cvs/bbs].synchro.net (1:103/705)