Configuring General SMTP Options

You can configure a variety of SMTP options using the General tab.

To configure general options:

  • Method of recipient validation: Recipient validation can be done using either SMTP look-ahead, Configuration Synchronization, or directory services. It can also be turned off, but this is not recommended unless you have a specific requirement.
    • Via downstream SMTP look-ahead (recommended): The Email Appliance's mail transfer agent (MTA ) uses SMTP recipient validation. The MTA will connect to the internal mail server to confirm that an address exists.

      In most cases, this form of recipient validation is preferable because it does not require an LDAP query that is comprehensive enough to include all addresses that should be accepted. Instead, the Email Appliance accepts or rejects messages, based on a response from the Microsoft Exchange server about whether the recipient is valid.

      • Advanced: Click this button to open the Advanced Recipient Validation Settings dialog box, and configure options for caching of recipient data. The default settings are applicable for most organizations. Do not adjust these settings or clear the cache unless there is a special requirement.
        • Expire negative responses after: Enter the frequency with which failed address verifications are expired from the cache. The default is 3 days.
        • Refresh negative responses every: Enter the frequency with which failed address verifications are refreshed. The default is 3 hours.
        • Expire positive responses after: Enter the frequency with which successful address verifications are expired from the cache. The default is 31 days.
        • Refresh positive responses every: Enter the frequency with which successful address verifications are refreshed. The default is 7 days.
        • Clear Cache: Deletes all cached results, positive and negative.
        • Reset to Defaults: Restores the factory settings.
    • Via Configuration Sync: You can maintain lists of some configuration data, including recipient validation, in text files. With Configuration Synchronization you can use the SCP protocol to sync those lists to the Email Appliance.
      Note
      If you are setting recipient validation using Configuration Synchronization, you should SCP a copy of your SOPHOS_RECIPIENT_VALIDATION file to the Email Appliance before setting Method of recipient validation: to Via Configuration Sync. For more information, see the Configuration Synchronization Documentation.
    • Via directory services: The Email Appliance's mail transfer agent (MTA) uses directory services queries to determine if messages are addressed to valid recipients. You should ensure that your directory services settings are configured correctly.
    • Disable recipient validation: Turns off recipient validation. It is recommended that you do not disable recipient validation, unless you have specific requirements.
  • Global Message Size Limit: Reject attachments that exceed a maximum size. It is recommended that you choose the smallest possible size limit because processing multiple large attachments at the same time may reduce the performance of the appliance.

    Note
    Selecting Unlimited is not recommended, and should be avoided if possible.
  • MTA banner string: Optionally, enter a banner string that replaces the default string. This setting has two available template variables: %%HOSTNAME%% and %%VERSION%%. By default, the hostname of the Email Appliance is displayed, along with the appliance version.
  • MTA HELO string: Optionally, enter a HELO string (hostname or IP address) that replaces the default string. This setting has one available template variable: %%HOSTNAME%%. By default, the hostname of the appliance is displayed.