Send an email from ASP.NET Page

internal class Mailer
    {
        private const int Timeout = 180000;

        private readonly string _host;
        private readonly int _port;
        private readonly string _user;
        private readonly string _pass;
        private readonly bool _ssl;

        public string Sender { get; set; }
        public string Recipient { get; set; }
        public string Subject { get; set; }
        public string Body { get; set; }
        public string AttachmentFile { get; set; }

        public Mailer()
        {
            _host = ConfigurationManager.AppSettings["MailServer"];
            _port = int.Parse(ConfigurationManager.AppSettings["Port"]);
            _user = ConfigurationManager.AppSettings["MailAuthUser"];
            _pass = ConfigurationManager.AppSettings["MailAuthPass"];
            _ssl = Convert.ToBoolean(ConfigurationManager.AppSettings["EnableSSL"]);
        }

        public void Send()
        {
            // We do not catch the error here... let it pass direct to the caller
            Attachment att = null;
            var message = new MailMessage(Sender, Recipient, Subject, Body) {IsBodyHtml = true};
            var smtp = new SmtpClient(_host, _port);
            
            if (!String.IsNullOrEmpty(AttachmentFile))
            {
                if (File.Exists(AttachmentFile))
                {
                    att = new Attachment(AttachmentFile);
                    message.Attachments.Add(att);
                }
            }

            if (_user.Length > 0 && _pass.Length > 0)
            {
                smtp.UseDefaultCredentials = false;
                smtp.Credentials = new NetworkCredential(_user, _pass);
                smtp.EnableSsl = _ssl;
            }

            smtp.Timeout = Timeout;
            smtp.Send(message);

            if (att != null)
                att.Dispose();
            message.Dispose();
            smtp.Dispose();
        }
    }

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Apart from the solution suggested by binaryevo, I would like to add one more thing.

Encrypt your <appSettings> section of Web.Config for better security.

Agreed with gery128, security is of utmost importance.

Your code must be fine, but its giving me some errors. Let me tell you I am quite new to ASP.NET, which is why also I need help. So please tell me why am I getting these errors, attached.
Errors.png

1)  Your button, BtCheckMail doesnt have an event associated with the button click.  Open up
design view of your webform and double click the button to resolve this.  It will take you to codebehind where the event will be created.

2)  Add the following to the top of the class in the using statements section:

using System.Net.Mail;

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Sorry but I still find the errors appearing. I am attaching the code and the errors, plus I have also opened the event on Button, but if I try to use Send over there, it does not accept. Yes I've yet not added the SMTP link, which I can only try once my code is error free.

Thanks.
SendMail.zip

Thanks, sorry for delayed response. Got busy travelling and in an assignment.
My programmer could make really good use of it. Works, thanks.