Thanks again Sabahattin
I've checked the information as you suggested. The postmaster account is a username: admin without a domainname.co.uk The local domains are included in the list: apsarchaeology; apsarchaeology.co.uk; lincsheritage; lincsheriatge.org and there are no filters setup which forward mail from the admin (Postmaster) account.
With regard to documentation and how subscriptions are requested, it would IMO, be more friendly to replace [full name] with [your name]. When I first saw this I thought it was requesting the 'full name' of the list as opposed to assuming an 'alias' which may have been used in the <list-name>. I know that those who are used to this may think it's obvious, but newbies will struggle with this.