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да, согласно RFC 821, команда VRFY предназначена для проверки наличия почтового ящика без непосредственной отправки письма. Но при настройке безопасности почтового сервера её (а также команду expn) часто отключают или заменяют синтаксической проверкой адреса получателя.
Bambarbia добавил [date]1052648651[/date]:
7.3 VRFY, EXPN, and Security
As discussed in section 3.5, individual sites may want to disable
either or both of VRFY or EXPN for security reasons. As a corollary
to the above, implementations that permit this MUST NOT appear to
have verified addresses that are not, in fact, verified. If a site
disables these commands for security reasons, the SMTP server MUST
return a 252 response, rather than a code that could be confused with
successful or unsuccessful verification.
Returning a 250 reply code with the address listed in the VRFY
command after having checked it only for syntax violates this rule.
Of course, an implementation that "supports" VRFY by always returning
550 whether or not the address is valid is equally not in
conformance.
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