Can't send file via SMTP protocol

[razorqhex]

@JonB, I wrote an error handler and this is what it outputs.

It seems to me that the problem is in this block of code:

        QByteArray boundary = "boundary_12345";
	QByteArray messageData;
	messageData.append("From: <YOUR_MAIL>\r\n");
	messageData.append(QString("To: <%1>\r\n").arg(ui->lEdit_addrFrom->text()).toUtf8());
	messageData.append(QString("Subject: %1\r\n").arg(subject).toUtf8());
	messageData.append("\r\n");
	messageData.append(QString(body).toUtf8() + "\r\n.\r\n");
	messageData.append(QString("Content-Type: multipart/mixed; boundary=%1\r\n").arg(boundary).toUtf8());
	messageData.append("\r\n");
	messageData.append(QString("--%1\r\n").arg(boundary).toUtf8());
	messageData.append("Content-Type: text/plain\r\n");
	messageData.append("\r\n");
	messageData.append(body.toUtf8());
	messageData.append("\r\n");
	messageData.append(QString("--%1\r\n").arg(boundary).toUtf8());
	messageData.append(QString("Content-Disposition: attachment; filename=\"%1\"\r\n").arg(QFileInfo(fileName).fileName()).toUtf8());
	messageData.append(QString("Content-Type: %1\r\n").arg(mime.name()).toUtf8());
	messageData.append("Content-Transfer-Encoding: base64\r\n");
	messageData.append("\r\n");
	socket.flush();
	messageData.append(fileData.toBase64());
	messageData.append("\r\n");
	messageData.append(QString("--%1--\r\n").arg(boundary).toUtf8());
	socket.write(messageData);
	socket.flush();

But I don't know exactly what the problem is.

[razorqhex]

@jsulm, Hello. I connected an error handler and wrote the debugger output above

[ChrisW67]

@razorqhex Your mail data is malformed (see my previous)

This is what a well-formed SMTP conversation should look like:

EHLO host.example.com
MAIL FROM: sender@example.com
RCPT TO: recipient@example.com
DATA
From: sender@example.com
To: recipient@example.com
Subject: Test email
Content-Type: multipart/mixed; boundary="test-boundary"

This is the preamble.  It is to be ignored, though it 
is a handy place for mail composers to include an 
explanatory note to non-MIME compliant readers. 
--test-boundary
Content-Type: text/plain; charset=utf-8

Body text

--test-boundary
Content-Disposition: attachment; filename="test.png"
Content-Type: image/png
Content-Transfer-Encoding: base64
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--test-boundary
This is the epilogue.  It is also to be ignored.

.
QUIT

[razorqhex]

@ChrisW67, I rewrote the code like this:

QByteArray boundary = "my_boundary";
QByteArray message;
message.append(QString("From: ").toUtf8() + QString(from).toUtf8() + QString("\r\n").toUtf8());
message.append(QString("To: %1").arg(ui->lEdit_addrFrom->text()).toUtf8() + QString(to).toUtf8() + QString("\r\n").toUtf8());
message.append("Subject: " + QString(subject).toUtf8() + "\r\n");
message.append("MIME-Version: 1.0\r\n");
message.append("Content-Type: multipart/mixed; boundary=" + boundary + "\r\n\r\n");

// Body
message.append("--" + boundary + "\r\n");
message.append("Content-Type: text/plain\r\n\r\n");
message.append(QString(body).toUtf8() + "\r\n\r\n");

// Attachment
message.append("--" + boundary + "\r\n");
message.append("Content-Disposition: attachment; filename=\"" + fileInfo.fileName().toUtf8() + "\"\r\n");
message.append("Content-Type: " + mime.name().toUtf8() + "; name=\"" + fileInfo.fileName().toUtf8() + "\"\r\n");
message.append("Content-Transfer-Encoding: base64\r\n\r\n");
message.append(fileData.toBase64() + "\r\n\r\n");

// Completing a message
message.append("--" + boundary + "--\r\n");

socket.write(message);
socket.write(".\r\n");
socket.flush();

And then I get a message with the correct attachment. But it still gets an error in this function:

//Message
if (!socket.waitForBytesWritten()) {
	qDebug() << "Error MESSAGE on SMTP-server";
	return;
}

if (!socket.waitForReadyRead()) {
	qDebug() << "Error";
	return;
}

And with all this, the error handler is not called.

Is it still a mistake in the structure of the message or what? I don't understand anything in this world

[SimonSchroeder]

@razorqhex said in Can't send file via SMTP protocol:

And then I get a message with the correct attachment. But it still gets an error in this function:

waitForBytesWritten() has a default value of 30 seconds as a timeout. If your operation takes longer than 30 seconds this function will return false and you'll see "Error MESSAGE on SMTP-server".

[razorqhex]

@SimonSchroeder, I know, but the fact is that without any pauses, the waitForBytesWritten () function immediately executes

[SimonSchroeder]

@razorqhex Then you should try qDebug() << socket.errorString(); to figure out what's happening.

[razorqhex]

@SimonSchroeder, this command show me "Unknown error"

[ChrisW67]

@razorqhex This could be because your call to QAbstractSocket::flush() has already written all the bytes to the underlying operating system. You then wait for more bytes to be written but there are none so you time out.

[razorqhex]

@ChrisW67, Yes! You're right! Thank you very much. The error was only that the logic of the code was incorrect.

I have corrected the structure of creating a message:

    QByteArray boundary = "my_boundary";
    QByteArray message;
    message.append(QString("From: ").toUtf8() + QString(from).toUtf8() + QString("\r\n").toUtf8());
//    message.append(QString("To: %1").arg(ui->lEdit_addrFrom->text()).toUtf8() + QString(to).toUtf8() + QString("\r\n").toUtf8());
    message.append(QString("To: ").toUtf8() + QString(to).toUtf8() + QString("\r\n").toUtf8());
    message.append("Subject: " + QString(subject).toUtf8() + "\r\n");
    message.append("MIME-Version: 1.0\r\n");
    message.append("Content-Type: multipart/mixed; boundary=" + boundary + "\r\n\r\n");

    // Body
    message.append("--" + boundary + "\r\n");
    message.append("Content-Type: text/plain\r\n\r\n");
    message.append(QString(body).toUtf8() + "\r\n\r\n");

    // Attachment
    message.append("--" + boundary + "\r\n");
    message.append("Content-Disposition: attachment; filename=\"" + fileInfo.fileName().toUtf8() + "\"\r\n");
    message.append("Content-Type: " + mime.name().toUtf8() + "; name=\"" + fileInfo.fileName().toUtf8() + "\"\r\n");
    message.append("Content-Transfer-Encoding: base64\r\n\r\n");
    message.append(fileData.toBase64() + "\r\n\r\n");

    // Completing a message
    message.append("--" + boundary + "--\r\n");
    //====================================================================================

    socket.write(message);
    socket.write(".\r\n");
//    socket.flush();

And also removed socket.flush(); when sending the MESSAGE command and when sending the QUIT command

And now everything works as it should. Once again thank you very much.

Now there is only one problem left to fix. Some SMTP servers do not understand Ukrainian and Russian encodings. Incomprehensible letters are shown instead of Cyrillic

UPD: I also corrected the encoding.
Where is the comment BODY
Instead of a line

message.append("Content-Type: text/plain\r\n\r\n");

Need to add

message.append("Content-Type: text/plain; charset=UTF-8\r\n\r\n");

And above, where the addressee is formed, you need instead of this line

message.append("Content-Type: multipart/mixed; boundary=" + boundary + "\r\n\r\n");

Write this line:

message.append("Content-Type: multipart/mixed; charset=UTF-8; boundary=" + boundary + "\r\n\r\n");

Thank you all for your help :)