Question

我想向超过1个人发送电子邮件。为什么这段代码显示此消息：“参数''不能为空字符串参数名称：to”？

connection.Open();
OleDbCommand command1 = new OleDbCommand();
command1.Connection = connection;
string cq = "Select Email From student where S_ID in(select S_ID FROM studentbook where DateDiff('d',[Issue_Date], NOW())=31) ";
command1.CommandText = cq;
OleDbDataAdapter da1 = new OleDbDataAdapter(command1);
DataTable dt1 = new DataTable();
da1.Fill(dt1);

foreach (DataRow row in dt1.Rows)
{
    string email = row["Email"].ToString();
    MessageBox.Show("Trying to send email ");

    using (MailMessage mm = new MailMessage("cuet.library12@gmail.com", email))
    {
        mm.Subject = "Attention please,renew your book";
        mm.Body = string.Format("1 month over,you should renew or return the book");

        mm.IsBodyHtml = true;
        SmtpClient smtp = new SmtpClient();
        smtp.Host = "smtp.gmail.com";
        smtp.EnableSsl = true;
        System.Net.NetworkCredential credentials = new System.Net.NetworkCredential();
        credentials.UserName = "xxxxxxxxxxxxx";
        credentials.Password = "xxxxxxxxxx";
        smtp.UseDefaultCredentials = true;
        smtp.Credentials = credentials;
        smtp.Port = 587;
        smtp.Send(mm);
        MessageBox.Show("Email sent successfully");
    }
}

Answer 1

从数据表中获取电子邮件地址后，请检查电子邮件是否为空。如果它为空则继续下一行。

string email = row["Email"].ToString();
if(String.IsNullOrEmpty(value) || value.Trim().Length == 0)
{
    continue;
}

Answer 2

您必须添加至少一个收件人：

mm.To.Add("email@example.com");

您还可以添加多个收件人。

Answer 3

试试这个：

mm.To.Add(new MailAddress("addres1@emailserver.com"));
mm.To.Add(new MailAddress("addres2@emailserver.com"));

请勿忘记在以下地址添加地址：

mm.From = new MailAddress("addres3@emailserver.com"));

如果您要在BCC发送电子邮件，可以使用：

mm.Bcc.Add(new MailAddress("addres1@emailserver.com"));
mm.Bcc.Add(new MailAddress("addres2@emailserver.com"));

^{来源：msdn.microsoft.com}

Answer 4

我猜你从datatable获得的电子邮件可能为null或为空。因此，在继续发送电子邮件之前，请务必检查空/空字符串。

if(String.IsNullOrEmpty(value))
    continue;

此外，如果您要向多个收件人发送相同的电子邮件，则不要在foreach循环中执行所有操作，而是在mm.To.Add("email address to send to");中添加收件人，然后最后发送电子邮件。

connection.Open();
varcommand1 = new OleDbCommand();
command1.Connection = connection;
varcq = "Select Email From student where S_ID in(select S_ID FROM studentbook where DateDiff('d',[Issue_Date], NOW())=31) ";
command1.CommandText = cq;
varda1 = new OleDbDataAdapter(command1);
vardt1 = new DataTable();
da1.Fill(dt1);
using (var mm = new MailMessage())
{
    foreach (DataRow row in dt1.Rows)
    {
        varemail = row["Email"].ToString();
        if(string.IsNullOrWhitespace(email))
            continue;
        mm.Bcc.Add(email);   
    }
    mm.From.Add("SenderEmailAddress");   
    mm.Subject = "Attention please,renew your book";
    mm.Body = string.Format("1 month over,you should renew or return the book");

    mm.IsBodyHtml = true;
    SmtpClient smtp = new SmtpClient();
    smtp.Host = "smtp.gmail.com";
    smtp.EnableSsl = true;
    var credentials = new System.Net.NetworkCredential();
    credentials.UserName = "xxxxxxxxxxxxx";
    credentials.Password = "xxxxxxxxxx";
    smtp.UseDefaultCredentials = true;
    smtp.Credentials = credentials;
    smtp.Port = 587;
    smtp.Send(mm);
}

一次发送多封电子邮件

4 个答案: