Sending mail "on behalf of" in exchange server 2010

Question

I am trying to send a mail using Exchange Server 2010 and System.Net.Mail.SmtpClient.I have given appropriate permission to the user on all the mailboxes. However, the mail sending fails ( without any exception in SendAsync method ). Instead, if I give Send As permission on the mailboxes, the mail sending succeeds. Is it possible to send "on behalf of" mails from Exchange Server without using Exchange APIs

Answer 1

MailMessage class exposes two properties: From and Sender

Setting Sender to address1 and From to address2 will send a mail which will read as "address1 on behalf of address2"

Answer 2

MailMessage message = new MailMessage();

message.From = new MailAddress("fromthepersonwho@sentthis.com");