If the Mailing List is in Text or Spreadsheet form containing hundreds of email addresses??
Subject: Text and spreadsheet are somewhat different…
For text files, you can open the file (e.g. using the Open statement), read it in a line at a time, and write code to figure out what to do with the characters. Of course the details vary greatly depending how the data are formatted.
For spreadsheets, it depends what type of spreadsheet it is. MS Excel has an OLE automation interface that lets you read information out of the cells.
Once you’ve got the data into variables, you would need to create a contact document out of it. The CreateDocument method will let you do this, but contact documents contain a bunch of fields, so you should probably take a sample that was created manually, and use this tool to generate code for it, then substitute in your values. Unless some kind person has created a class for managing contact records.
Subject: I found a simpler method to import mailing list
This method is importing the mailing list to the Note Client as a new Mail Group!
Inside Notes Client 8, choose Mail, then Group, then new Group. Copy the whole spreadsheet’s email address column or text file’s email addresses content. Paste into the newly create Group input space!!! WOW! GUESS WHAT! Notes Client will sort the email addresses and eliminate duplicated addresses! Then, save the Group into a new name!
When you start a new email letter promotion, just send email to this email Group! However, remember this is a group mail and is considered as Spam in most case and may be blocked as junk by your customers! 
For a more efficient promotion, importing from mailing list to separate contact is highly recommended!