By mailing list, I meant list of physical mail box addresses!
It did cross my mind that I should have been more explicit, but I thought saying just 'mail' and not 'email' would be fine. Sorry I forgot this is 2010! haha
Anyhow the information you gave me was helpful in knowing other aspects of the software, many thanks!
So I will describe the potential experience in general terms:
1- Visitor creates a custom product e.g. a brochure
2- Visitor orders the product
3- During the ordering phase, visitor selects a checkbox "To be sent via letter mail"
4- A second form element asking something like "How is the mail list provided?" with options like "Mail list has already been submitted or exists" or "Mail list will be submitted"
5- Visitor exits website after submitting cart
6- Administrator processes the order if everything ready & correct (job ready + mailing list exists)
7- Administrator pauses the order if something wrong (e.g. no mailing list has been submitted yet).