Message Size Limit: This setting tells the module to reject all incoming messages that are larger than the specified limit.
Message Recipients Limit: This setting limits the number of recipients for each incoming message. Specifying a lower value makes your server less attractive for spammers.
Non-Client Sender: Limits: Use this option to specify a time period and the limit on the number of message recipients. For each non-client IP address the SMTP module counts all messages coming from that IP address, and all recipients specified for those messages. If the total number of all recipients specified during the set time period exceeds the set limit, new recipients are rejected with a temporary code, forcing the sending server to retry sending messages to those recipients later. If a sender has completed a successful SMTP AUTH operation that allows the sender to relay via the CommuniGate Pro server, the recipients sent via that connection are not counted. This setting can be used to protect your Server from spammers that send one message or a batch of messages to a large number of users of your system. On the other hand, if a large number of your users is subscribed to some mailing list, this option can cause delays for messages coming from that list.
Non-Client Sender: Delay Prompt: Use this option to specify the delay time between the moment when an SMTP connection is accepted from a non-client address and the moment when the Server responds with an initial prompt. This delay can be used to force spam-sending programs to disconnect from your Server. Normal servers should still be able to transfer mail, as the RFC2821 standard requires them to wait 5 minutes for the initial prompt, and most servers do wait at least 3 minutes. When this setting has a non-zero value, the Server checks if any data line has been received from the sender before the initial SMTP prompt is sent. If the sender has sent some data without waiting for an initial Server prompt, an error message is returned to the sender and the connection is closed. The Prompt Delay is introduced only for connection made to the port 25.
Note: if you start to use long Prompt Delays, expect to see your Server using much more SMTP Input channels, as each SMTP transaction becomes longer.
Non-Client Sender: Disconnect Use this option to specify how many protocol errors the SMTP module should detect before it drops the connection with the sender. This feature protects your Server from spammers that try various E-mail addresses (dictionary attack), causing "unknown account" errors. The SMTP module places the network addresses of disconnected senders into the Temporarily Blocked Addresses list. The SMTP module rejects new connections from the Temporarily Blocked Addresses. Note: the module does not block a "failed sender" network address if that address is a Client IP Add