XnetSolutions SX-GATE, Руководство пользователя

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14.5.3 SPAM/Virus/Malware 353
This feature might also affect legitimate emails which by mistake
use a misconfigured sender address. This sometimes occurs
with computer generated emails of badly configured online
registrations or shopping systems.
for existance
An email won't be accepted if its sender domain doesn't exist in DNS.
for valid mailserver
In this mode SX-GATE additionally determines the IP address of the mail server
for this domain. In case it is invalid, delivery is refused. The test is not performed
on connections from internal source IPs.
If DNS reports a permanent error when resolving the sender domain (e.g. domain does
not exist), SX-GATE's mail server will refuse delivery. The sender which may be a
user's mail client program or an other mail server is in charge of dealing with the error.
If it's the SX-GATE mail client which tried to deliver a mail
retrieved from a POP server, the mail will be discarded without
notice. As the sender domain is invalid, returning an error to
the sender makes no sense. Delivery to the local administrator
contradicts the purpose of defeating SPAM.
However DNS might also report a temporary problem resolving the sender domain (e.g.
name server unreachable). There are two different behaviours, depending on whether
the SX-GATE mail client has been enabled in the configuration or not. If it is not used,
the SX-GATE mail server will refuse delivery with a temporary error. Depending on
its configuration, the sending mail server might retry delivery later before notifying the
sender. If the DNS problem has been solved in the meantime, the mail will be accepted.
If in contrast the SX-GATE mail client is enabled, emails will be accepted despite of
temporary DNS errors. This keeps the SX-GATE mail client from retrieving the same
mail over and over again if the reported temporary DNS error is in fact a permanent one.
Reject mails sent with own domain as sender
Many unsolicited emails use the recipient domain also in the sender address. With this
option inbound emails will be rejected if the sender address contains one of the local
domains. This check is not performed for authenticated connections and connections
from IPs listed below "Local IP addresses" in menu "Modules > Mail Server > SMTP
settings" on tab "Relay control". Also emails retrieved from a POP server are not
affected.