It might be the case that it's useful for an MTA to have an option to
skip MX lookup for specific destinations because of DNS brokenness at
those destinations. But this seems to me to be outside of the scope of
By the same token, discussions of gatewaying to non-Internet systems could be
considered "outside the standard". But RFC 2821 devotes many pages to
discussing this sort of thing.
Skipping MX lookup is not acceptable as a general
practice, nor is it something we want to encourage.
I never implied that it was acceptable. In fact I'm fairly sure I said
the exact opposite.
In general, it's always been acceptable to configure an MTA to handle
mail in some special-case way for specific domains where there was
specific knowledge such that the special-case handling made sense for
those domains. The MX-then-A lookup is what you should do in the
absence of any such knowledge.
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