412 Chapter 7 • Managing the Edge Transport Server When an SMTP session is established between an external SMTP server and the edge transport server, the fi lters listed in Figure 7.29 are applied in a specifi c order. In the next section, we’ll look at the order in which the various fi lters are applied. Connection Filtering When an SMTP session is established to the Edge Transport server, the fi rst fi lter applied is the Connection Filter. The Connection Filtering agent will fi rst check whether the IP address of the external SMTP server is listed on the IP Allow list, which is shown in Figure 7.31. Figure 7.30 Installing the Filtering Agents on the Hub Transport Server NOTE You can specify individual IP addresses as well as a range of IP addresses under the Allowed Addresses tab on the IP Allow List Properties page (see Figure 7.31). Managing the Edge Transport Server • Chapter 7 413 If the IP address is listed here, the SMTP server will be allowed to connect and transmit e-mail messages to the Exchange 2007 organization, but the e-mail messages will be sent to the Sender Filtering agent for further processing. If the IP address of the SMTP server isn’t listed on the IP Allow list, the Connection Filtering agent will check to see whether the server is listed on the IP Block list shown in Figure 7.32. Figure 7.31 The IP Allow List 414 Chapter 7 • Managing the Edge Transport Server If the IP address of the SMTP server is listed on the IP Block list, connections from the server will be refused. NOTE A neat little improvement to the IP Address Block list is that you now can set an expiration date and time for an individual IP address or a range of IP addresses. This was not possible with Exchange Server 2003 SP2. If the IP address of the SMTP server isn’t listed on either the IP Allow list or the IP Block list, the Connection Filtering agent will check to see whether the IP address is allowed by any IP Allow list provider you have specifi ed (see Figure 7.33). Figure 7.32 The IP Block List Managing the Edge Transport Server • Chapter 7 415 Figure 7.33 IP Allow List Providers An IP Allow list provider is a provider that maintains a list of sender domains/IP addresses that you can rely on for sending legitimate e-mail messages and not spam. You can specify multiple IP Allow list providers and even specify how the providers’ features should interpret the returned status. If the SMTP server isn’t listed on any of these lists, the Connection Filtering agent will do one last check before it allows the SMTP connection. It will check whether the server is listed on any real-time block lists (RBLs) you have specifi ed under the Providers tab on the IP Block List Providers Properties page (see Figure 7.34). 416 Chapter 7 • Managing the Edge Transport Server Figure 7.34 Adding an IP Block List Provider . addresses that you can rely on for sending legitimate e-mail messages and not spam. You can specify multiple IP Allow list providers and even specify how the providers’ features should interpret the. Server • Chapter 7 413 If the IP address is listed here, the SMTP server will be allowed to connect and transmit e-mail messages to the Exchange 2007 organization, but the e-mail messages will be. neat little improvement to the IP Address Block list is that you now can set an expiration date and time for an individual IP address or a range of IP addresses. This was not possible with Exchange