10291 Recon and testing

Recon and testing notes take whilst looking into fix for Issue 10291.

recon-notes.md: Contains notes on the OS, and postfix configuration of the machine (prox34) listed in the issue. It also contains some notes on the default posfix configs applied on a fresh install.

testing-notes.md: Contains notes on the steps taken to reproduce the issue, and the proposed fix.

error-repro: Contains all the files used for reporducing the issue, along with a sample of the logs generated as part of the testing.

error-fix: Contains all the files used for testing the proposed fix.