Many thanks for you very speedy reply!
There were only 6 recipients of the email, but a few test ones (single recipients) haven't gone through either.
Although I've created many sites using WP, I am not really familiar with CRON management as I've never had a reason before (to my knowledge) to mess about with it!
I've since noticed in the CampTix help file that ships with the plugin, it states:
Note that the e-mails will not be sent out straight away, but rather grouped into tasks, which are carried out using a cron schedule.
But they're still marked as pending after 2 days! The trouble is, I'm not sure how to change or check what my cron settings are? Or how to alter them to send emails from the Camptix module straight away?
I created a test user using my own email address, and received the standard 'username and password' & 'New user registration' emails into my inbox within seconds, which shows email from the site/server is working ok.
I also enabled debugging as you suggested and sent a test email from the Camptix Ticketing plugin, but couldn't see any debug output during the process?
I'm sure it must be something simple, but I'm just a bit surprised that no-one appears to be having the same issue?
If you have any other ideas for me i'd be very grateful.
I really appreciate your help with this!