You can enable restrictions so that the MTA does not accept messages when non standard or other disapproved behavior is exhibited by an incoming SMTP client. These restrictions provide some protection against ill-behaved spam senders.
In addition, you can enable the following DNS-based BlackHole Lists:
reject_rbl_client dnsbl.njabl.org
reject_rbl_client cbl.abuseat.org
reject_rbl_client bl.spamcop.net
reject_rbl_client dnsbl.sorbs.net
reject_rbl_client sbl.spamhaus.org
reject_rbl_client relays.mail-abuse.org
Important: Before setting these restrictions, identify what type of mail is received outside of your mail system. If a mail system that you want to receive mail from is poorly implemented, you might have to compromise your restrictions to accommodate their messages.
Procedure
1. Go to the Configure>Global Settings>MTA page.
2. Check the appropriate boxes in the Protocol Checks section to restrict the following SMTP protocol violators.
|
Option |
Description |
|---|---|
|
Hostname in greeting violates RFC (reject_invalid_helo_hostname) |
Reject the request when the hostname syntax is invalid. |
|
Client must greet with a fully qualified hostname (reject_non_fqdn_helo_hostname) |
Reject the request when the hostname is not in fully-qualified domain form. |
|
Sender address must be fully qualified (reject_non_fqdn_sender) |
Reject the request when the Mail From address is not in fully-qualified domain form. |
3. Check the appropriate boxes in the DNS checks section to enable DNS based restrictions.
|
Option |
Description |
|---|---|
|
Client's IP address (reject_unknown_client_hostname) |
Reject the request when the client address>name mapping fails, or when the name>address mapping fails, or if the name>address mapping does not match the client IP address. |
|
Hostname in greeting (reject_unknown_helo_hostname) |
Reject the request when the hostname has no DNS A or MX record. |
|
Sender's domain (reject_unknown_sender_domain) |
Rejects the request when this is not the final destination for the sender address and the Mail From domain has no DNS A or MX record, or a malformed MX record. |
4 In the List the RBLs section, add specific RBL types that should be enabled.
5. Click Save.
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