What does your correspondent need or want? One well established standard for exchanging contact information is the vCard which encapsulates many of the commonly used fields in a Contact entry. If a vCard suits you and your correspondent, this add-on: https://nic-nac-project.org/~kaosmos/morecols-en.html has a nifty feature for sending vCards as attachments. Then your correspondent can probably just add it to his address book. If you copy out single details, like name, address, email address phone no, then the other person has to insert each one into his address book by hand. If you open the Mailing List in your Address Book, you can probably drag each item out into the body of a new email message. But that's more work than necessary for you and for the recipient, who will need to add each one manually to his address book. With this add-on, you should be able to open the Mailing List by selecting it in the Address Book, then use ctrl+a to select all, then right-click and select "Send as vCard"; it will open a new message with all the selected Contacts attached. Lists in general don't have a standard presentation, so a List in one email client is only rarely useful in another. If you both use Thunderbird, you could use this add-on to export the List to a .tha or .thm file which another Thunderbird user could import.

Thanks very much. This is really helpful