I'm setting up a postfix mailserver. Only a handful (of about 6 domains ,
ie x...@dsta.gov.sg , x...@starnet.gov.sg, x...@ncssmsonbehalf.com.sg ,
x...@accenture.com ) are allowed to email to my postfix server.
>From security & efficiency (so as not to process too many emails)
point of view,
a) do I permit SMTP (Tcp 25) only to the above few domains) or do
I permit to all public Internet & use whitelisting to permit only
those few domains to send to me ?
b) how do I determine the source IP address of those domains besides
calling up those organizations to find out? Is there some kind of
lookup services to find out their addresses so that I can provide
these source addresses for our firewall administrator to permit
SMTP ?
I'm using dovecot to provide POP3 functionality as well so I'll need to
know those email clients' source IP addresses that connects to my
postfix server to empty emails from some of my postfix email accounts.
Thanks & apologies if these are basic questions
