Filter source IP addresses for SMTP connections
To provide additional security by allowing SMTP connection requests from authentic IP addresses and avoiding/rejecting requests from unsolicited IP addresses, filters can be defined in Message Connector.
Using the Source IP Filter field in Email Inbound via SMTP tab, Message Connector provides an option to define list of filters. Using these filters, SMTP connections to Message Connector are either allowed or denied. By default, no filter is defined and connections are allowed from all IP addresses.
Each line in the Source IP Filter field defines a filter and starts with an Allow or Deny keyword followed by the CIDR (Classless Inter-Domain Routing) notation of an IP range. These filters are compared with the source IP address of a request. If a source IP address falls in a category of a filter starting with Allow, the SMTP connection for that IP address is accepted.
For example, a filter Allow 10.20.30.0/24 allows request from IP addresses from 10.20.30.0 to 10.20.30.255. That is, any request from and source with IP address between 10.20.30.0 to 10.20.30.255 is allowed.
Additionally, if filters are defined but no filter matches with the incoming source IP address request, the request is denied. Else, the first matching filter defines whether the request should be allowed or denied.