We use ezmlm mailing list manager. The mailing list system has some predefined text as an automatic response to various mailing list tasks such as subscription and unsubscription confirmations, amongst other things.
You can edit and customise these text using the email interface.
Firstly, login to your Quadra Hosting control panel, and click on the mailing list in question. Pay attention to the options marked in rectangle below, to enable remote administration and editing of the text files.
Then make sure you've added your email address into the moderators list of this mailing list.
Next, send an email to firstname.lastname@example.org
You should receive a list of files / text that you can edit, and further instructions on how to edit them. For example, to see what's inside and edit the 'top' file, send a blank email to email@example.com - here the ".top" means you want to see / edit the 'top' text.