Without knowing the specifics of this...
Is the domain name for your e-mail address used on your cPanel account for web hosting
If so do you actually use cPanel for your e-mail or is the e-mail handled by another server?
If a domain name is parked on the cPanel account then any software running on the web account will not send e-mail to an external e-mail server for that domain name, as the cpanel server just assumes it is handling the e-mail without checking the MX record to verify this. In this case logging in to Horde (e-mail) on the c-panel server should turn up the missing e-mails. (it is possible for our hosting dept to sort this situation on a per user/domain basis however if you have confirmed this is indeed the case)
This theory however falls down when you say that regular member lists (presumably on the same hosting account) work to this address. All I could assume in that instance is that the e-mail is somehow configured differently between the two types of e-mail (eg it sends using the external e-mail server for regular mailing lists, but uses the inbuilt sendmail on the cPanel box for administrator e-mail)
Another possibility of course is that your administrator e-mail is getting binned by a spam filter - but I would assume thats easy enough to check/disprove?
Kindest regards,
James Sweet
http://www.zen.co.uk