At present I can prevent sending email to the collected address by
$config['enableMail'] - default: true
Set this to false to prevent XenForo from sending any emails.
I would rather not collect it at all. I saw someone had created a work around for this in a previous version - 1.2 i think - but I cannot find it again
As I recall they were generating a unique disposable email for each login, but that's a bit beyond my skills set. I am afraid I might kill the software So I will leave well enough alone for now. Thanks for your help