I found that my quota notification script wasn't working as expected. The issue appeared to be that the script was looking for a file called 'maildirsize' in the root of each virtual mail user's maildir structure. Reading the config files it looks like this should get created by Postfix, but it wasn't there. The following lines from the /etc/postfix/main.cf file summarise what I found.

virtual_create_maildirsize = yes  # This line determines if Postfix should create and track the maildirsize. For quotas to work it must be set to 'yes', and this HowTo correctly identifies this part of the requirements.

virtual_mailbox_extended = yes # This is where the mistake is.
virtual_maildir_extended = yes # This is what it should read.

For those who missed it, the mailbox should be maildir.

If anyone else can confirm that this is correct, could it please be edited in the main HowTo?

Thanks for all your great work. Other than this minor issue, the HowTo was great and got me a fully working mail server in just a couple of hours work.