MailMessage mm = new MailMessage();
string strEmails = “abcccs22@domain.com; sd22321@gasd3mail.com; s2s33@gdasdsdmail.com;”;

string[] emails = strEmails.Split(‘;’);
foreach (string email in emails)
{
if (email.Trim() != string.Empty)
{
mm.ReplyToList.Add(new MailAddress(email));
}
}