Just for the records. The IBM Redbook "Lotus Domino 6 spam survival Guide" does recommend to use SMTPMaxforRecipients in the notes.ini to reduce the effectiveness of harvesting email addresses. Chapter 4.5.2 in: http://www.redbooks.ibm.com/redbooks/pdfs/sg246930.pdf

This parameter does not seem to work, neither in 5.x nor in 6.x. The problem is known as SPR TMEN62PF8B if you like to request a fix.