How do I prevent my ESA from being used as an open relay?
To secure your ESA from being used as an open relay, make sure that you have specified the recipient domain(s) in the Recipient Access Table (RAT) of your Public listener(s) and that the "ALL" entry is configured to "Reject". RAT entries can be added via the GUI, on the Mail Policies tab. Below is an example showing how to add a domain, "example.com" to the RAT via the CLI.
mail.example.com> listenerconfig Currently configured listeners: 1. InboundMail (on PublicNet, 172.19.1.80) SMTP TCP Port 25 Public 2. OutboundMail (on PrivateNet, 172.19.2.80) SMTP TCP Port 25 Private Choose the operation you want to perform: - NEW - Create a new listener. - EDIT - Modify a listener. - DELETE - Remove a listener. - SETUP - Change global settings. > edit Enter the name or number of the listener you wish to edit. > 1 Name: InboundMail Type: Public Interface: PublicNet (172.19.1.80/24) TCP Port 25 Protocol: SMTP Default Domain: Max Concurrency: 1000 (TCP Queue: 50) Domain Map: Disabled TLS: No SMTP Authentication: Disabled Bounce Profile: Default Use SenderBase For Reputation Filters and IP Profiling: Yes Footer: None LDAP: Off
Choose the operation you want to perform: - NAME - Change the name of the listener. - INTERFACE - Change the interface. - LIMITS - Change the injection limits. - SETUP - Configure general options. - HOSTACCESS - Modify the Host Access Table. - RCPTACCESS - Modify the Recipient Access Table. - BOUNCECONFIG - Choose the bounce profile to use for messages injected on this listener. - MASQUERADE - Configure the Domain Masquerading Table. - DOMAINMAP - Configure domain mappings. > rcptaccess Recipient Access Table There are currently 1 recipients. Default Access: REJECT< Choose the operation you want to perform: - NEW - Create a new entry. - EDIT - Modify an entry. - IMPORT - Import a table from a file. - EXPORT - Export the table to a file. > new Enter the recipient address for this entry. Hostnames such as "example.com" and "[18.104.22.168]" are allowed. Partial hostnames such as ".example.com" are allowed. Usernames such as "postmaster@" are allowed. Full email addresses such as "firstname.lastname@example.org" or "email@example.com" are allowed. Separate multiple addresses with commas. > example.com Select the action to apply to this address: 1. Accept 2. Reject > Would you like to specify a custom SMTP response? [N]> Would you like to bypass receiving control for this entry? [N]> Recipient Access Table There are currently 2 recipients. Default Access: REJECT Choose the operation you want to perform: - NEW - Create a new entry. - EDIT - Modify an entry. - DELETE - Remove an entry. - PRINT - Display all entries. - IMPORT - Import a table from a file. - EXPORT - Export the table to a file. - CLEAR - Remove all entries. > print ironport.com ACCEPT ALL REJECT
Notice that the "ALL" entry is configured to "REJECT". This entry causes the system to reject messages from any host that is not specifically configured to be accepted.