Can the text "L-Soft list server at [...] ([version number])" be removed from mail coming from LISTSERV?

Yes, the PLAIN_FROMLINE site configuration variable allows you to do this.  (This is not supported prior to LISTSERV 14.3.)

PLAIN_FROMLINE is a Boolean variable (set to 1 or zero) which controls whether or not LISTSERV generates a plain From: line when sending administrative mail, e.g., setting this variable to "1" would result in

From: LISTSERV@LISTSERV.EXAMPLE.COM


rather than

From: "Example Company LISTSERV Server (16.0)" <LISTSERV@LISTSERV.EXAMPLE.COM>


Examples:

z/VM:

PLAIN_FROMLINE = 1

Unix:

PLAIN_FROMLINE=1

export PLAIN_FROMLINE

Win:

PLAIN_FROMLINE=1

Enabling PLAIN_FROMLINE overrides any setting made to MYORG=, since the organization name setting and release number will no longer be displayed.