Postfix smtpd_client_restrictions

Keeping known email abusers out is always desired. Postfix has a parameter which is specified in the main.cf file that allows you to refer to these lists.
The script I use is as follows…

smtpd_client_restrictions =
permit_mynetworks
permit_sasl_authenticated
reject_unauth_pipelining
reject_rbl_client cbl.abuseat.org
reject_rbl_client dnsbl.ahbl.org
reject_rbl_client dnsbl.sorbs.net
reject_rbl_client list.dsbl.org
reject_rbl_client sbl-xbl.spamhaus.org
#reject_rhsbl_client blackhole.securitysage.com
reject_rhsbl_client rhsbl.sorbs.net
permit

Note the commented out line

#reject_rhsbl_client blackhole.securitysage.com

See below
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Telnet your email server

Very often it is necessary to test that your SMTP server is working.
The easiest way to do this is with the telnet command.
This lets you talk directly to the email server in its own SMTP protocol script language.
Here’s how…
telnet server name or IP address 25
HELO aaaa
mail from: <tom@fromdomain.com>
rcpt to: <fred@todomain.com>
data
Enter your message text
.
quit
Along the way [...]

PostCast Server

This is an SMTP server like the one your ISP provides. It is targeted at Windows users and sells as a faster and more flexible alternative.
I don’t like to be negative about the efforts of others but, I do find it diffucult to see what advantage this server application gives you over the already available [...]