The message could not be sent to the SMTP server. The transport error code was 0x80040217. The server response was not available

Hello all,

First off, if there is a better place to post for an answer to this
question, please feel free to point me there.

I have some very strange behavior happening with my System.web.mail objects.
I was able to run my application fine for roughly 1500 email messages. The next time I tried sending mail, it stopped working with the message:
"
The message could not be sent to the SMTP server. The transport error code
was 0x80040217. The server response was not available

Description: An unhandled exception occurred during the execution of the
current web request. Please review the stack trace for more information
about the error and where it originated in the code.

Exception Details: System.Runtime. InteropServices .COMException: The message could not be sent to the SMTP server. The transport error code was
0x80040217. The server response was not available

Source Error:
An unhandled exception was generated during the execution of the
current web request. Information regarding the origin and location of the
exception can be identified using the exception stack trace below.
Stack Trace:
[COMException (0x80040211): The message could not be sent to the SMTP
server. The transport error code was 0x80040217. The server response was not available
]

[TargetInvocatio nException: Exception has been thrown by the target of an invocation.]
System.RuntimeT ype.InvokeDispM ethod(String name, BindingFlags invokeAttr, Object target, Object[] args, Boolean[] byrefModifiers, Int32 culture,
String[] namedParameters ) +0
System.RuntimeT ype.InvokeMembe r(String name, BindingFlags invokeAttr,
Binder binder, Object target, Object[] args, ParameterModifi er[] modifiers, CultureInfo culture, String[] namedParameters ) +473
System.Web.Mail .LateBoundAcces sHelper.CallMet hod(Object obj, String
methodName, Object[] args) +58

[HttpException (0x80004005): Could not access 'CDO.Message' object.]
System.Web.Mail .LateBoundAcces sHelper.CallMet hod(Object obj, String
methodName, Object[] args) +113
System.Web.Mail .CdoSysHelper.S end(MailMessage message) +1840
System.Web.Mail .SmtpMail.Send( MailMessage message) +150
Intranet.srcMai l.sendMailNow(S tring listID) in c:\documents and
settings\sean\v swebcache\srcfi leserver\intran et\srcmail.cs:1 28
Intranet.srcCom mon.fnSendMail( String strTo, String strSubject, String
strBody, String list_ID, String groupID, String Mailing) in c:\documents and settings\sean\v swebcache\srcfi leserver\intran et\srccommon.cs :257
Intranet.srcCom mon.doMail(Bool ean bTest, String strEmailAddress , String
txtBody, String txtSubject, String listID, String groupID, String Mailer) in c:\documents and
settings\sean\v swebcache\srcfi leserver\intran et\srccommon.cs :100
Intranet.TestMa ilToSignups.But ton1_Click(Obje ct sender, EventArgs e) in
c:\documents and
settings\sean\v swebcache\srcfi leserver\intran et\testmailtosi gnups.aspx.cs:1 2 3
System.Web.UI.W ebControls.Butt on.OnClick(Even tArgs e) +108

System.Web.UI.W ebControls.Butt on.System.Web.U I.IPostBackEven tHandler.RaiseP o stBackEvent(Str ing eventArgument) +57
System.Web.UI.P age.RaisePostBa ckEvent(IPostBa ckEventHandler
sourceControl, String eventArgument) +18
System.Web.UI.P age.RaisePostBa ckEvent(NameVal ueCollection postData) +33
System.Web.UI.P age.ProcessRequ estMain() +1277

-------------------------------------------------------------------------- -- ----

Version Information: Microsoft .NET Framework Version:1.1.432 2.573; ASP.NET Version:1.1.432 2.573 "

My question is this: What would cause this behaviour? I have since changed several lines of code to try to fix the problem, but have not had any
success. This has happened to me in the past and it seemed like rebooting
the server may have fixed it, not this time however.

Here's my code snippit:

public void sendMailNow(str ing listID)

{

MailMessage myMail = new MailMessage(); myMail.To = ToMail;

if(mBCC != "")

myMail.Bcc = mBCC;

myMail.From = FromMail;

myMail.Subject = mSubject;

myMail.BodyForm at = mFormat;

myMail.Body = mBody;

myMail.Fields["http://schemas.microso ft.com/cdo/configuration/smtpauthentica te"] = 1;

myMail.Fields["http://schemas.microso ft.com/cdo/configuration/sendusername"] = mUserName;

myMail.Fields["http://schemas.microso ft.com/cdo/configuration/sendpassword"] = mPassword;

SmtpMail.SmtpSe rver = mSMTPServer;

SmtpMail.Send(m yMail);

logMailnow(ToMa il,listID);

}