关于用asp.net发送电子邮件问题（内、外部邮件）？

using System;
using System.Web.Mail;namespace Common.Common
{
/// <summary>
/// CommonMail &#65397;&#65412;&#65429;&#65386;&#65426;&#65386;&#65419;&#65397;&#65411;&#65379;
/// </summary>
public class CommonMail
{
protected string m_MailFrom="";
protected string m_MailTo="";
protected string m_Subject="";
protected string m_Body="";
protected string m_Attachment=""; ///<summary>
///
///</summary>
public string MailFrom
{
get
{
return m_MailFrom;
}
set
{
m_MailFrom=value;
}
}
///<summary>
///
///</summary>
public string MailTo
{
get
{
return m_MailTo;
}
set
{
m_MailTo=value;
}
}
///<summary>
///
///</summary>
public string Subject
{
get
{
return m_Subject;
}
set
{
m_Subject=value;
}
}
///<summary>
///
///</summary>
public string Body
{
get
{
return m_Body;
}
set
{
m_Body=value;
}
}
///<summary>
///
///</summary>
public string Attachment
{
get
{
return m_Attachment;
}
set
{
m_Attachment=value;
}
}
public CommonMail()
{
//
// TODO: &#65428;&#65434;&#65396;&#65419;&#65396;&#65382;&#65420;&#64018;&#65427;&#65401;&#65401;&#65428;&#12539;&#65391;&#65418;&#63729;&#65410;&#65439;&#65404;&#65389;
//
}
public bool SendMail()
{
try
{
MailMessage mailObj = new MailMessage(); mailObj.From = this.m_MailFrom.ToString().Trim();
mailObj.To = this.m_MailTo.ToString().Trim();
mailObj.Subject =this.m_Subject.ToString().Trim();
mailObj.Body = this.m_Body.ToString().Trim();   
mailObj.BodyFormat=MailFormat.Html;

if(this.m_Attachment.ToString().Trim()!="")
{
mailObj.Attachments.Add(new MailAttachment(this.m_Attachment.ToString().Trim()));
}

SmtpMail.Send(mailObj);
return true;
}
catch
{
return false;
} }
}
}