Mail Transport Settings

This section impacts primarily the Postfix Mail Transport Agent (MTA) and applies to all servers (Master and Child) within the Mailborder cluster. 


Maximum Email Size

Any email that exceeds this size will not be accepted by the MTA. Mailborder does not send an error notice to the original sender. However, the sender will be notified by their own email server of the error. This method prevents backscatter


Maximal Queue Lifetime

As noted on the configuration page, this is how long each server will hold email in the event it cannot be delivered. For example, your internal email server is down and cannot accept email. 5 days is the standard. You may increase this if you are experiencing a prolonged outage. \


Realtime Blackhole Lists

The RBLs are processed at the Postfix level and rejections will not be displayed in the email log. Any remote sender will be notified of the rejection by their own email server. Again, this method prevents backscatter. You may add your own RBLs via the command line. Add them one per line to this file:



Reverse DNS Checks

This is one of the most basic of checks, but many email servers fail this check. This verifies that any remote server connecting to a Mailborder server has a valid reverse DNS record for their IP address. This is commonly referred to as a PTR record. 

While simple, this is a powerful check as many spammers do not have the ability to create PTR records for compromised systems. It is also one of the most basic administrative steps when standing up an email server. If you have a client or business partner failing this checks, it is recommended that you encourage them to create a valid PTR record for their email server rather than disabling this check. 


Rate Limit Exceptions

Mailborder automatically implements a sane rate limit for remote servers. It controls how often and how many emails can be sent within a certain time period. Spammers will try to send as many as possible in as short a period of time as possible. Rate limits slow the onslaught. However, you may have some business partners that send a large volume of valid email. To prevent them from being rate limited, enter the domain name of their server or IP address here. 


RBL Overrides

Sometimes legitimate servers end up on black lists. If this has happened to a business partner, add their domain or IP in this section and their servers will not be rejected for RBL reasons. 



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