How to resolve the error "the SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.57 " in C#?

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C#

SmtpClient

I am getting below error while trying to send mail in c#.
The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.57 Client not authenticated to send mail. [PN1PR01CA0073.INDPRD01.PROD.OUTLOOK.COM]
I have set EnablSSL property as true in the code.

What I have tried:

Code is as below:

MailMessage objMailMsg = new MailMessage();
MailAddress fromAddress = new MailAddress(Common.FromMail);
SmtpClient smtpClient = new SmtpClient();

int port = Common.SMTPPort;
string FileName = Common.EMAIL_FILE_PATH+objEmail.AttachedFileName;
string IPaddr = Common.SMTPServer;
objMailMsg.From = fromAddress;

string[] Toarray = objEmail.ToEmailId.Split(',');
foreach (string ToAddress in Toarray)
{
if (ToAddress.Trim() != string.Empty)
objMailMsg.To.Add(ToAddress.Trim());
}
if (objEmail.CCEmailId != null && objEmail.CCEmailId.Length > 0)
{
string[] Ccarray = objEmail.CCEmailId.Split(',');
foreach (string CcAddress in Ccarray)
{
if(CcAddress.Trim()!= string.Empty)
objMailMsg.CC.Add(CcAddress.Trim());
}
}

char[] chrDelim = new char[] { ',' };

foreach (string strSubstr in FileName.Split(chrDelim))
{
if (File.Exists(strSubstr))
{
Attachment objAttachment = new Attachment(strSubstr);
objMailMsg.Attachments.Add(objAttachment);
}
}
objMailMsg.Subject = objEmail.EmailSubject;
objMailMsg.Body = objEmail.EmailBody;
objMailMsg.IsBodyHtml = true;
if (port == 0)
{
port = 25;

}
Common.WriteDDSLog("Email Sent :-"+FileName);
smtpClient.Port = port;
smtpClient.Host = IPaddr;
smtpClient.EnableSsl = true;
smtpClient.Send(objMailMsg);