Delphi + Indy: Connection closed gracefully

问题:

Using D7 + Indy 10 latest build.

My code is using TIdSMTP to send email. I keep getting "Connection closed gracefully" at some end-users, and the email is never sent.

The code is like:

try
~~~~
~~~~
_idSMTP := TIdSmtp.Create;
with _idSMTP do
begin
  Host := 'myhost';
  Connect;
  try
    Send(_EmailMsg);
    Result := True;
  except
    on E: Exception do
    begin
      MsgDlgErr(Self.Handle, E.Message)
    end
  end;
end;
finally
 _idSMTP.Disconnect;
 _idSMTP.Free;
end;

Any advice?

回答1:

Read all about it on http://www.swissdelphicenter.ch/en/showarticle.php?id=1

EIdConnClosedGracefully is an exception signaling that the connection has been closed by the other side intentionally. This is not the same as a broken connection which would cause a connection reset error. If the other side has closed the connection and the socket is read or written to, EIdConnClosedGracefully will be raised by Indy. This is similar to attempting to read or write to a file that has been closed without your knowledge.

In some cases this is a true exception and your code needs to handle it. In other cases (typically servers) this is a normal part of the functioning of the protocol and Indy handles this exception for you. Even though Indy catches it, when running in the IDE the debugger will be triggered first. You can simply press F9 to continue and Indy will handle the exception, but the constant stopping during debugging can be quite annoying. In the cases where Indy catches the exception, your users will never see an exception in your program unless it is run from the IDE.

回答2:

In my case the error was caused because I used a sender email address from a different domain than the one hosted by the smtp server, that's why the smtp server rejected the connection.

回答3:

In my experience, in case of AT&T server, it rejects an email address which is not @att.net address in the MAIL FROM. More info can be determined by logging the error using TIdLogEvent for these users that receive it, otherwise the error report is rather vague - if the disconnect (Connection closed gracefully) occurs right after the MAIL FROM then it might indicate a server policy rejecting an email with the domain which it doesn't host as explained by Toni as well.

Otherwise the "Connection closed gracefully" error means that an attempt is being made to read/write to socket that has been closed by the peer intentionally - in your case, peer is the SMTP server you connect to. It is different than the "Connection reset" error which indicates a broken connection. In both cases, the connection is no longer present and you can't read/write anymore to it.