They appear to be stackable, though there may be a limit to the stack.  However, as mentioned, I cannot find this defined in the manuals, so no idea as to any limitations or requirements.

________________________________________
From: LISTSERV site administrators' forum [[log in to unmask]] on behalf of Pete Weiss [[log in to unmask]]
Sent: Friday, July 05, 2013 3:28 PM
To: [log in to unmask]
Subject: Re: Send= (listname)

I don't know if multipleSEND= are stackable (append) or override one another.  Nevertheless, one of
the lists that I operate called listA has this as a SEND


* Send= Private,(listB)

listB subscribers can post to listA.

/Pete

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