The reasons that younger MUA's do not offer that are social, not technical.
It has never been particularly difficult technically for a MUA to work
without a smarthost/MSA, ...
Well, for fairly loose definitions of "work", since I've never seen an MUA
that did retries on soft failure.
Now the question is essentially moot, since any legitimate mail sent direct
from an MUA is swamped in the flood from bots.
R's,
John
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