c#使用System.Web.Mail或System.Net.Mail发送邮件，解决使用SSL协议发送超时

一般我们使用System.Web.Mail或System.Net.Mail发送邮件，但这类命名空间支持Explicit SSL但是不支持Implicit SSL，所以如果发送使用如QQ邮箱的SSL 465端口，将会报超时错误。

System.Web.Mail代码

System.Web.Mail.MailMessage mail = new System.Web.Mail.MailMessage();
try
{
mail.To = "收件人邮箱";
mail.From = "发件人邮箱";
mail.Subject = "subject";
mail.BodyFormat = System.Web.Mail.MailFormat.Html;
mail.Body = "<font color='red'>body</font>";

mail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate", "1"); //basic authentication
mail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendusername", "发件人邮箱"); //set your username here
mail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendpassword", "发件人邮箱密码"); //set your password here
mail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpserverport", 465);//set port
mail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpusessl", "true");//set is ssl
System.Web.Mail.SmtpMail.SmtpServer = "smtp.qq.com";
System.Web.Mail.SmtpMail.Send(mail);
//return true;
}
catch (Exception ex)
{
ex.ToString();
}

System.Net.Mail代码

using (MailMessage mail = new MailMessage()) { mail.From = 
                new MailAddress(BlogSettings.Instance.Email, name); 
                mail.ReplyTo = new MailAddress(email, name); 
                mail.To.Add(BlogSettings.Instance.Email); 
                mail.Subject = BlogSettings.Instance.EmailSubjectPrefix + " " + Resources.labels.email.ToLower() + " - " + subject; 
                mail.Body = "<div style=\"font: 11px verdana, arial\">"; 
                Attachment attachment = new Attachment(txtAttachment.PostedFile.InputStream, txtAttachment.FileName); 
                mail.Attachments.Add(attachment); 
                try { message.IsBodyHtml = true;
                    message.BodyEncoding = Encoding.UTF8; 
                    var smtp = new SmtpClient(BlogSettings.Instance.SmtpServer); 
                    if (!string.IsNullOrEmpty(BlogSettings.Instance.SmtpUserName)) 
                    { smtp.Credentials = new NetworkCredential(BlogSettings.Instance.SmtpUserName, BlogSettings.Instance.SmtpPassword); } 
                    smtp.Port = BlogSettings.Instance.SmtpServerPort; 
                    smtp.EnableSsl = BlogSettings.Instance.EnableSsl; 
                    smtp.Send(message);
                    OnEmailSent(message); } catch (Exception ex) { } }

以上两种在遇到使用Implicit SSL的SMTP服务均会报超时错误。 解决方法，使用CDO.Message发送邮件，添加引用C:\Windows\System32\cdosys.dll

代码：

CDO.Message objMail = new CDO.Message(); 
            try { 
                objMail.To = "接收邮件账号"; 
                objMail.From = "发送邮件账号"; 
                objMail.Subject = "subject";//邮件主题 
                objMail.HTMLBody = "";//邮件内容 
                objMail.Configuration.Fields["http://schemas.microsoft.com/cdo/configuration/smtpserverport"].Value = 465;//设置端口 
                objMail.Configuration.Fields["http://schemas.microsoft.com/cdo/configuration/smtpserver"].Value = "smtp.qq.com"; 
                objMail.Configuration.Fields["http://schemas.microsoft.com/cdo/configuration/sendemailaddress"].Value = "发送邮件账号"; 
                objMail.Configuration.Fields["http://schemas.microsoft.com/cdo/configuration/smtpuserreplyemailaddress"].Value = "发送邮件账号"; 
                objMail.Configuration.Fields["http://schemas.microsoft.com/cdo/configuration/smtpaccountname"].Value = "发送邮件账号"; 
                objMail.Configuration.Fields["http://schemas.microsoft.com/cdo/configuration/sendusername"].Value = "发送邮件账号"; 
                objMail.Configuration.Fields["http://schemas.microsoft.com/cdo/configuration/sendpassword"].Value = "发送邮件账号登录密码"; 
                objMail.Configuration.Fields["http://schemas.microsoft.com/cdo/configuration/sendusing"].Value = 2; 
                objMail.Configuration.Fields["http://schemas.microsoft.com/cdo/configuration/smtpauthenticate"].Value = 1; 
                objMail.Configuration.Fields["http://schemas.microsoft.com/cdo/configuration/smtpusessl"].Value = "true";//这一句指示是否使用ssl 
                objMail.Configuration.Fields.Update(); objMail.Send(); } catch (Exception ex) 
            { throw ex; } finally { } 
            System.Runtime.InteropServices.Marshal.ReleaseComObject(objMail); 
            objMail = null;

以上基本可以解决邮件功能，当然如果需要发送附件，ASP.NET可以先临时保存文件，C/S架构则直接操作附件属性即可。 当然如果可以使用25端口，则不存在以上问题，但如国内阿里云封了25端口，服务器又没有端口映射，只能使用Implicit SSL 的 465端口，这中方式可以算是最简单的了，不使用系统外组件完成。