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smtp fails to send mail sometimes in c#

I have gone through some questions on this topic. All the answers relate when sending email fails all the time. In my case, it fails only sometimes with exception message:
The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.57 SMTP; Client was not authenticated to send anonymous mail during MAIL FROM...
If I try second time it works. I'm using the following configuration.
using (MailMessage mail = new MailMessage())
{
mail.From = new MailAddress("emailid", "displayname");
mail.To.Add("TOAddress");
mail.Subject = subject1;
mail.Body = body1;
mail.IsBodyHtml = true;
using (SmtpClient smtp = new SmtpClient("Outlook.office365.com", 587))
{
smtp.UseDefaultCredentials = false;
smtp.Credentials = new NetworkCredential("emailid", "password");
smtp.EnableSsl = true;
smtp.Send(mail);
}
}
checked a similar question here , given solutions not working.

Try this(second answer): Gmail Error :The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required
I used this code to send the email:
MailMessage msg = new MailMessage();
msg.From = new MailAddress("sender#gmail.com");
msg.To.Add("receiver#gmail");
msg.Subject = "Hello";
msg.Body = "Test";
SmtpClient smt = new SmtpClient();
smt.Host = "smtp.gmail.com";
System.Net.NetworkCredential ntcd = new NetworkCredential();
ntcd.UserName = "sender#gmail.com";
ntcd.Password = "senderPassword";
smt.Credentials = ntcd;
smt.EnableSsl = true;
smt.Port = 587;
smt.Send(msg);
Also check if your virus scanner doens't block your email from sending.

Unable to send email using Mailkit from a xamarin.android app

I am not able to send email from a xamarin.android app using MailKit library of jstedfast.
I am using the following code :
try
{
//From Address
string FromAddress = "from_sender#gmail.com";
string FromAdressTitle = "Email Title";
//To Address
string ToAddress = "to_receiver#gmail.com";
string ToAdressTitle = "Address Title";
string Subject = "Subject of mail";
string BodyContent = "Body of email";
//Smtp Server
string SmtpServer = "smtp.gmail.com";
//Smtp Port Number
int SmtpPortNumber = 587;
var mimeMessage = new MimeMessage();
mimeMessage.From.Add(new MailboxAddress(FromAdressTitle, FromAddress));
mimeMessage.To.Add(new MailboxAddress(ToAdressTitle, ToAddress));
mimeMessage.Subject = Subject;
mimeMessage.Body = new TextPart("plain")
{
Text = BodyContent
};
using (var client = new SmtpClient())
{
client.Connect(SmtpServer, SmtpPortNumber, false);
// Note: only needed if the SMTP server requires authentication
// Error 5.5.1 Authentication
client.AuthenticationMechanisms.Remove("XOAUTH2");
client.Authenticate("from_sender#gmail.com", "password");
client.Send(mimeMessage);
Console.WriteLine("The mail has been sent successfully !!");
Console.ReadLine();
client.Disconnect(true);
}
}
catch (Exception ex)
{
string message = ex.Message;
}
When I run this code from my app, it throws an exception:
MailKit.Security.AuthenticationException
What I am missing in this code. Can anybody help me out !

Use MAILMESSAGE class.
using System.Net.Mail;
.
MailMessage mail = new MailMessage("example#gmail.com", "example#gmail.com", "Title","Body");
SmtpClient client = new SmtpClient();
client.Host = ("smtp.gmail.com");
client.Port = 587; //smtp port for SSL
client.Credentials = new System.Net.NetworkCredential("example#gmail.com", "password");
client.EnableSsl = true; //for gmail SSL must be true
client.Send(mail);

Cannot get c# to send email from hotmail

When I run this code, I get an error :
System.Net.Mail.SmtpException: Failure sending mail. --->
System.Net.WebException: Unable to connect to the remote server
---> System.Net.Sockets.SocketException: A connection attempt failed because the connected party did not properly respond after a period of
time, or established connection failed because connected host has
failed to respond 65.55.163.152:587
Code :
static void Main(string[] args)
{
string smtpAddress = "smtp.live.com";
int portNumber = 587;
bool enableSSL = true;
string emailFrom = "xxxxx#hotmail.co.uk";
string password = "xxxxxxxxxxx";
string emailTo = "myname#businessemail.co.uk";
string subject = "Daily Email Check";
string body = "Email reached business exchange server from an external hotmail email account";
using (MailMessage mail = new MailMessage())
{
mail.From = new MailAddress(emailFrom);
mail.To.Add(emailTo);
mail.Subject = subject;
mail.Body = body;
mail.IsBodyHtml = false;
try
{
using (SmtpClient smtp = new SmtpClient(smtpAddress, portNumber))
{
smtp.Credentials = new NetworkCredential(emailFrom, password);
smtp.EnableSsl = enableSSL;
smtp.Send(mail);
}
}
catch (Exception e)
{
Console.WriteLine("Error\n\n {0}", e);
Console.ReadKey();
}
}
}

Try this;
using System.Net.Mail;
...
MailMessage mail = new MailMessage("xxxxx#hotmail.co.uk", "myname#businessemail.co.uk");
SmtpClient client = new SmtpClient();
client.Port = 25;
client.DeliveryMethod = SmtpDeliveryMethod.Network;
client.UseDefaultCredentials = false;
client.Host = "smtp.live.com";
mail.Subject = "Daily Email Check";
mail.Body = "Email reached business exchange server from an external hotmail email account";
client.Send(mail);

The server rejected the sender address

I was able to send emails with local smtp but when trying to send with gmail, it isnt working.
ERROR:
"The server rejected the sender address. The server response was: 530 5.7.0
Must issue a STARTTLS command first. pj7sm14546972pbb.96 - gsmtp\r\n"
C#:
public static void SendEmail()
{
MailMessage mailMsg = new MailMessage();
SmtpClient smtpClient = new SmtpClient();
mailMsg.From = "donotreply#admin.com"; //also tried smtpusername here
mailMsg.To = strToAddress;
mailMsg.Subject = strSubject;
mailMsg.Body = strBody;
smtpClient.Port = 587;
smtpClient.EnableSsl = true;
smtpClient.Credentials = new NetworkCredential(smtpusername, smtppassword);
//smtpusername & smtppassword are valid gmail credentials
SmtpMail.SmtpServer = "smtp.gmail.com";
SmtpMail.Send(mailMsg);
}

If the EnableSsl property is set to true, and the SMTP mail server
does not advertise STARTTLS in the response to the EHLO command, then
a call to the Send or SendAsync methods will throw an SmtpException.
https://msdn.microsoft.com/en-us/library/system.net.mail.smtpclient.enablessl(v=vs.110).aspx

sending mail failure in asp.net using c# [duplicate]

This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Sending email in .NET through Gmail
This mail code is working in localhost i.e on my computer but when i uopload it on server it is not working.
The error is : Failure sending mail. please tell me where is the problem.
if (Session["userinfo"] != null)
{
lblTest.Text = Session["userinfo"].ToString();
MailMessage msg = new MailMessage();
msg.From = new MailAddress("shop.bcharya#gmail.com");
msg.To.Add(new MailAddress("bcc#dr.com"));
msg.To.Add(new MailAddress("info#yzentech.com"));
msg.Subject = "Mail from BcharyaCorporation.online shopping site";
msg.Body = ""+lblTest.Text+" wants to buy some products. please contact with him/her";
SmtpClient sc = new SmtpClient();
sc.Host = "smtp.gmail.com";
// sc.Port = 25;
sc.Credentials = new NetworkCredential("shop.bcharya#gmail.com", "mypassword");
sc.EnableSsl = true;
try
{
sc.Send(msg);
lblPayment.Text = "Sorry. Currently we are out of online payment service. We will contact you for payment process. Thank you for buying this product.";
}
catch (Exception ex)
{
lblPayment.Text=ex.Message.ToString();
Response.Write(ex.Message);
}
}

For gmail mail settings add Port number too
sc.Port = 587;
after this line
sc.Host = "smtp.gmail.com";

Only use port 587 and SSL if the SMTP server supports that (GMail and Hotmail for example). Some servers just use port 25 and no SSL.

Use below method and then check :
SmtpClient sc = new SmtpClient(string); //sends e-mail by using the specified SMTP server

You can use this below given code for sending email. Here sending the error details through email is one method. Try this code for sending email.
using System.Web.Mail
public static bool SendErrorEmail(string to, string cc, string bcc, string subject, string body, MailPriority priority, bool isHtml)
{
try
{
using (SmtpClient smtpClient = new SmtpClient())
{
using (MailMessage message = new MailMessage())
{
MailAddress fromAddress = new MailAddress(“yourmail#domain.com”, “Your name”);
// You can specify the host name or ipaddress of your server
smtpClient.Host = “mail.yourdomain.com”; //you can specify mail server IP address here
//Default port is 25
smtpClient.Port = 25;
NetworkCredential info = new NetworkCredential(“yourmail#domain.com”, “your password”);
smtpClient.DeliveryMethod = SmtpDeliveryMethod.Network;
smtpClient.UseDefaultCredentials = false;
smtpClient.Credentials = info;
//From address will be given as a MailAddress Object
message.From = from;
message.Priority = priority;
// To address collection of MailAddress
message.To.Add(to);
message.Subject = subject;
// CC and BCC optional
if (cc.Length > 0)
{
message.CC.Add(cc);
}
if (bcc.Length > 0)
{
message.Bcc.Add(bcc);
}
//Body can be Html or text format;Specify true if it is html message
message.IsBodyHtml = isHtml;
// Message body content
message.Body = body;
// Send SMTP mail
smtpClient.Send(message);
}
}
return true;
}
catch (Exception ee)
{
Logger.LogError(ee, “Error while sending email to ” + toAddress);
throw;
}
}