> My first suspicion was that the multi-layered MIME structure was
> confusing LISTSERV and preventing
> it from recognizing parts that were nested two levels deep.

LISTSERV is supposed to handle that.

> The whole problem might actually hinge on a peculiarity of the boundary
> delimiters generated by
> Lotus Notes. As shown in the sample below, it generates delimiters
> containing white space.

I think this is it. It was fixed in 15.0:

145-0024 06/09/20 [B] Allow spaces in MIME boundaries

  Eric