Application please send me an E-mail
Some thoughts about the code itself.


In general method names recommended as Pascal Case so sendEmail should ideally be named SendEmail
I might consider trying to make the class a bit more configurable so that it could be extended in more ways without being modified.  For example if you wanted to send a text email, or you wanted to send an email using a different server.


The modified code might look like:

public class Emailer
{
    // Required for emailer to work
    private readonly string _host;
    private readonly int _portNumber;

    // Optional configurable options
    public bool IsHtml { get; set; }
    public MailPriority Priorty { get; set; }

    public Emailer()
        : this("mailexchanger_String", 25)
    {

    }

    public Emailer(string host, int portNumber)
    {
        _host = host;
        _portNumber = portNumber;

        IsHtml = true;
        Priorty = MailPriority.High;
    }

    public void SendEmail(
        string bodyText,
        string sender,
        List&lt;string&gt; recipientAddresses)
    {
        SendEmail(
            bodyText,
            new MailAddress(sender),
            recipientAddresses.Select(p =&gt; new MailAddress(p)).ToList());
    }

    public void SendEmail(
        string bodyText,
        MailAddress sender, 
        List&lt;MailAddress&gt; recipientAddresses)
    {
        // .NET 4.0 only for SmtpClient disposing
        using (var smtpClient = new SmtpClient(_host, _portNumber))
        {
            using (var mailMsg = new MailMessage())
            {
                mailMsg.From = sender;
                mailMsg.Body = bodyText;
                mailMsg.IsBodyHtml = IsHtml;
                mailMsg.Priority = Priorty;                        
                recipientAddresses.ForEach(p =&gt; mailMsg.To.Add(p));

                smtpClient.Send(mailMsg);
            }
        }
    }
}


You can also configure an SMTP client via the .config.  In that case
you do not need to provide the connection details in the code but instead can configure it via the .config file.

For an MVC.net application that may be in the web.config or for a desktop application that might be in an app.config.

&lt;system.net&gt;
&lt;mailSettings&gt;
  &lt;smtp from="&lt;fromaddress&gt;"&gt;
    &lt;network host="mailexchanger_String" password="??" userName="??" port="25" enableSsl="true" defaultCredentials="false" /&gt;
  &lt;/smtp&gt;
&lt;/mailSettings&gt;
&lt;/system.net&gt;


This means that you could create the SMTP client on Emailer creation and then dispose it as necessary.  In this case the code might look like

internal class Emailer : IDisposable
{
    // Our smtp client that will be disposed
    private readonly SmtpClient _smtpClient;

    // Optional arguments
    private bool _isHtml = true;
    public bool IsHtml { get { return _isHtml;  } set { _isHtml = value; } }

    private MailPriority _mailPriority = MailPriority.High;
    public MailPriority Priorty { get { return _mailPriority;  } set { _mailPriority = value; } }

    public Emailer()
    {
        _smtpClient = new SmtpClient();
    }

    public Emailer(string host, int portNumber)
    {
        _smtpClient = new SmtpClient(host, portNumber);
    }

    public void SendEmail(
        string bodyText,
        string sender,
        List&lt;string&gt; recipientAddresses)
    {
        SendEmail(
            bodyText,
            new MailAddress(sender),
            recipientAddresses.Select(p =&gt; new MailAddress(p)).ToList());
    }

    public void SendEmail(
        string bodyText,
        MailAddress sender, 
        List&lt;MailAddress&gt; recipientAddresses)
    {
        using (var mailMsg = new MailMessage())
        {
            mailMsg.From = sender;
            mailMsg.Body = bodyText;
            mailMsg.IsBodyHtml = IsHtml;
            mailMsg.Priority = Priorty;                        
            recipientAddresses.ForEach(p =&gt; mailMsg.To.Add(p));

            _smtpClient.Send(mailMsg);
        }                
    }

    public void Dispose()
    {
        _smtpClient.Dispose(); // Or not if using &lt; .NET 4.0
    }
}


And used like:

using(var emailer = new Emailer())
{
    emailer.SendEmail(
        bodyText,
        sender,
        "sendtome"
    );
}