Unable to send an email to multiple addresses/recipients using C#

Question

I am using the below code, and it only sends one email - I have to send the email to multiple addresses.

For getting more than one email I use:

string connectionString = ConfigurationManager.ConnectionStrings["email_data"].ConnectionString; OleDbConnection con100 = new OleDbConnection(connectionString); OleDbCommand cmd100 = new OleDbCommand("select top 3 emails  from bulk_tbl", con100); OleDbDataAdapter da100 = new OleDbDataAdapter(cmd100); DataSet ds100 = new DataSet(); da100.Fill(ds100);      for (int i = 0; i < ds100.Tables[0].Rows.Count; i++)     //try     {         string all_emails = ds100.Tables[0].Rows[i][0].ToString();         {             string allmail = all_emails + ";";             Session.Add("ad_emails",allmail);             Response.Write(Session["ad_emails"]);             send_mail();         }     } 

and for sending the email I use:

string sendto = Session["ad_emails"].ToString();  MailMessage message = new MailMessage("[email protected]", sendto, "subject", "body"); SmtpClient emailClient = new SmtpClient("mail.smtp.com"); System.Net.NetworkCredential SMTPUserInfo = new System.Net.NetworkCredential("abc", "abc"); emailClient.UseDefaultCredentials = true; emailClient.Credentials = SMTPUserInfo; emailClient.Send(message); 

Answer 1

The problem is that you are supplying a list of addresses separated by semi-colons to the MailMessage constructor when it only takes a string representing a single address:

A String that contains the address of the recipient of the e-mail message.

or possibly a list separated by commas (see below).

Source

To specify multiple addresses you need to use the To property which is a MailAddressCollection, though the examples on these pages don't show it very clearly:

message.To.Add("[email protected], [email protected]")); 

The e-mail addresses to add to the MailAddressCollection. Multiple e-mail addresses must be separated with a comma character (",").

MSDN page

so creating the MailMessage with a comma separated list should work.

Answer 2

This is what worked for me. (recipients is an Array of Strings)

//Fuse all Receivers var allRecipients = String.Join(",", recipients);  //Create new mail var mail = new MailMessage(sender, allRecipients, subject, body);  //Create new SmtpClient var smtpClient = new SmtpClient(hostname, port);  //Try Sending The mail try {     smtpClient.Send(mail); } catch (Exception ex) {     Log.Error(String.Format("MailAppointment: Could Not Send Mail. Error = {0}",ex), this);     return false; }