To get around that previous mentioned potential blocks, phishing writers are now creating emails that do not contain any obvious malicious links. They don't ask users to visit bogus Websites or to install unexpected software. Rather, they attempt to fool a user or system admin into opening up holes in the company's network defenses.
Here's an example of one of these messages, sent to me by my friend and CISSP, Bob McCoy. It was addressed to him directly and appeared to come from his company's email service provider. (For brevity and safety, I've removed the vendor names, authentic-looking graphics, and links from the message.)
Dear Valued Customer,
We are pleased to announce the go-live date for a new Data Center, scheduled to go live on April 19, 2010.
Please update your firewall rules to allow SMTP traffic on port 25 from the following IP address ranges:xxx.xxx.xxx.xxx/xx (xxx.xxx.xxx.xxx - xxx.xxx.xxx.xxx)xx.xxx.xxx.xx/xx (xx.xxx.xxx.xx - xx.xxx.xxx.xxx)
If you have settings on your e-mail server which control the IPs which are allowed to connect for e-mail relay please confirm that those settings are updated as well.
We will be able to test and verify connections one week prior to April 19, 2010. Additionally, we will be proactively running connection tests prior to the launch on behalf of all customers, and contacting you directly if we are unable to connect to any of your domains from ALL specified IP addresses for that domain.
Prior to the launch of the new IP addresses, we recommend that you set up and configure the Deferral Notification alerting feature for your domains using the Deferral Notification option on the Domain properties page in the Admin Center. The Deferral Notification alert feature sends a message to you when a customized threshold has been met or exceeded for deferred e-mail in your domain. After the new IP addresses are launched, this feature will help to ensure that e-mail sent to your domains is not deferred because of unsuccessful connection attempts to your network, and that you alerted in the event that e-mail is being deferred beyond your acceptable limits. For more information on how to set up the Deferral Notification alert feature, see the Admin Center Guide in the Resource Center.
Please refer to the Configuration subtab of the Administration Center for a complete list of IPs which should be allowed to connect to your environment at any time.