Peter,
why not? There's To, CC, BCC etc:
http://www.weonlydo.com/Smtp/Help/WODSMTPLib~SmtpMsg~To.html
http://www.weonlydo.com/Smtp/Help/WODSMTPLib~SmtpMsg~CC.html
http://www.weonlydo.com/Smtp/Help/WODSMTPLib~SmtpMsg~BCC.html
Multiple recipients can be separated by ;
Please note that except for changing email (so recipient sees other CC and To recipients) you can also set MailTo property
http://www.weonlydo.com/Smtp/Help/WODSMTPLib~wodSmtp~MailTo.html
that causes recipients to be specified with RCPT TO command on SMTP server, while leaving original message intacts.