postfix

I have a postfix SMTP relay buried deep in a network behind proxy servers, all the infrastructure [sadly] is IPv4 only. This works, yet one ends up with many log messages like:

connect to smtp.office365.com[2603:1036:304:2857::2]:587: Network is unreachable

The server attempts if IPv6 result from the DNS lookup first. So let's make postfix use IPv4 only.

postconf -e inet_protocols=ipv4

That's it! No more "unreachable" log messages.

When testing applications one of the concerns is always that their actions don't effect the real-world. One aspect of that this is sending e-mail; the last thing you want is the application you are testing to send a paid-in-full customer a flurry of e-mails that he owes you a zillion dollars. A simple, and reliable, method to avoid this is to adjust the Postfix server on the host used for testing to bury all mail in a shared folder. This way:

Creating an in house signing [aka CA] certificate is a common practice; this allows you to generate free cerficates for internal use. For Windows hosts distributing this CA certificate to all the clients and relevant servers can be accomplished using Active Directory GPOs. Certificate management on LINUX hosts on the other hand has always been a swamp of tedium where the certificates often need to be configured into each client or service. Recent distributions have eased this process considerably by including a quasi-standardized set of scripts and certificate store locations.