C # How to test whether the smtpclient client successfully connects to the smtpserver?

Refer to my blog post for a souvenir, especially the hash code-use SMTP to send emails in. net.

Reference and sort out chinafcl

In smtpclient, only the email address, password, and SMTP server address are provided. How can I test whether the email address and password are correct? (Similar to the test connection function of the mail client)

Private bool checksmtp (string smtpserver, int port, string username, string password)
{
Tcpclient = new tcpclient (smtpserver, Port );
Networkstream stream = tcpclient. getstream ();

If (! Waitefor (stream, "220") return false;

Sendcommand (stream, "HELO 211.152.50.xxx \ r \ n ");
If (! Waitefor (stream, "250") return false;

Sendcommand (stream, "auth login \ r \ n ");
If (! Waitefor (stream, "334") return false;

Sendcommand (stream, base64encode (username) + "\ r \ n ");
If (! Waitefor (stream, "334") return false;

Sendcommand (stream, base64encode (password) + "\ r \ n ");
If (! Waitefor (stream, "235") return false;

Return true;

}

Private bool waitefor (networkstream stream, string strcode)
{
Int streamsize;
Byte [] readbuffer = new byte [1024];
Streamsize = stream. Read (readbuffer, 0, readbuffer. Length );
String returnvalue = encoding. Default. getstring (readbuffer). substring (0, streamsize );

Console. writeline (returnvalue );

Return returnvalue. substring (0, 3). Equals (strcode );
}
Private void sendcommand (networkstream stream, string strcmd)
{
Byte [] writebuffer;

Writebuffer = encoding. Default. getbytes (strcmd );

Stream. Write (writebuffer, 0, writebuffer. Length );

}

Private string base64encode (string Str)
{
Byte [] barray;
Barray = encoding. Default. getbytes (STR );
Return convert. tobase64string (barray );
}