Sending mail in .Net – just a few tips

Sending mails in .Net is actually very easy. In just a few lines you can send you very first mail automatically:

MailMessage mailMessage = new MailMessage();
mailMessage.To.Add(new MailAddress("myfriend@domain.com"));
mailMessage.Subject = "Adrian's blog rocks";
mailMessage.IsBodyHtml = true;
mailMessage.Body = "Check out this cool blog";
SmtpClient emailClient = new SmtpClient();
emailClient.Send(mailMessage);

That’s pretty much it! You’ll probably ask about the from email address and the SMTP server. These are configured in Web.config:

<configuration>
    ...
    <system.net>
    ...
    <!-- the mail settings used to send emails -->
    <mailSettings&gt
      <smtp deliveryMethod="Network" from="admin@domain.com"&gt
        <network host="smtp.domain.com"/&gt
      </smtp&gt
    <mailSettings&gt
    ...
    </system.net>
    ...
<configuration>

But anyway you can specify them too:

mailMessage.From = new MailAddress("admin@domain.com");
SmtpClient emailClient = new SmtpClient("smtp.domain.com");

Multiple recipients

If you want to send your message to multiple recipients, just use message.To.Add. So if you have a string with semicolon(;) separated email addresses here’s the code for you:

String emailAddresses = "a.friend@domain.com; another.friend@domain.com";
foreach (String to in emailAddresses.Split(new char[] {';'}, StringSplitOptions.RemoveEmptyEntries)) 
{
    mailMessage.To.Add(new MailAddress(to));
}

The same goes for CC, BCC, ReplyTo.

Flag a message

Are you a fan of those follow up message? Let me show you how to send them. The idea is pretty simple: those mail messages have two headers – one for the flag and one for the follow up date. To get/set headers of a mail message just use the Headers property.

mailMessage.Headers["X-Message-Flag"] = "Follow up";
mailMessage.Headers["Reply-By"] = DateTime.Now.AddDays(1).ToString("ddd, dd MMM yyyy HH:mm:ss %K");

The above will send a message to be followed up one day later from the sending time. The format of the date in the Reply-By header is specified in RFC822 and if you want to know how to format a date in .Net, see this. If you just want to send your message use what I compiled for you.

The invalid subject error

If you try to set the message subject to a string that contains invalid characters you will get the error System.Net.Mail: The specified string is not in the form required for a subject. This can be easily fixed with

mailMessage.Subject = Regex.Replace(subject, @"[^ -~]", "");