Use of this feature is best limited to low-volume sites. Looking up every address in the
bestmx map can cause numerous DNS enquiries. At high-volume sites, the magnitude of
extra DNS enquiries can adversely tax the system and network.
There is also a risk to this feature. Someone could create an MX record for your site
without your knowledge. Bogus mail might then be accepted at your site without your
permission:
bogus.site.com. IN MX 0 your.real.domain
Here, mail to bogus.site.com would be sent to your site, where the name bogus.site.com
would be looked up with FEATURE(bestmx_is_local). Your sendmail would find itself listed
as the MX for bogus.site.com and so would accept the bogus mail and attempt to deliver it
locally. If the bogus name were designed to discredit you, it could be set to
sex.bogus.site.com, for example, and mail to root@sex would be delivered to you without
you knowing the reason.
17.8.9 FEATURE(bitdomain)
Convert BITNET addresses into Internet addresses Deprecated
This FEATURE(bitdomain) is deprecated because its functionality can be handled by the
newer FEATURE(domaintable) (?§17.8.16 on page 621). In case you still need to use
FEATURE(bitdomain), we continue to describe it here.
Many Internet hosts have BITNET addresses that are separate from their Internet
addresses. For example, the host icsi.
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