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Connect to SMTP / POP / IMAP Server through Credential without Password


My current environment : Aspose.Email version

Found this article statement under Connecting to POP3 Server, without further elaboration on the properties. How is this work in Aspose?

Connecting with an APOP Server
APOP is an extended version of the POP3 server setting that encrypts your username and password, and uses authentication mechanism designed to protect your POP3 account’s password when checking email. APOP authentication does not require the account password to be sent as plain text to the POP3 mail server.

I have experienced few mail server which does not require Authentication when sending and receiving e-mails.


Thank you for contacting Aspose Support team.

We are sorry but we could not find any other related information in this regard. One possibility is the usage of UseDefaultCredentials but that seem to send the default credentials with the requests. We have further requested our Product team to share their feedback with us in this regard and will update you here as soon as some information is available in this regard.

Kindly assist, need the solution in urgent.
For your further finding, this is my sample code, same credential, only work for Microsoft .NET smtp wrapper.
System.Net.Mail.SmtpClient smtp (Working fine)
smtp.Host = Server;
smtp.Port = Port;
smtp.UseDefaultCredentials = false;
if (string.IsNullOrEmpty(Login) || string.IsNullOrEmpty(Password))
smtp.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;
smtp.Credentials = new System.Net.NetworkCredential(Login, Password);

if (EnableSSL)
smtp.EnableSsl = true;
smtp.EnableSsl = false;

setupSmtpClient(Aspose.Email.Mail.SmtpClient mSmtpClient (Not Working)
mSmtpClient.Host = Server;
mSmtpClient.Port = Port;
mSmtpClient.UseDefaultCredentials = false;
mSmtpClient.AuthenticationMethod = SmtpAuthentication.Auto;
if (!string.IsNullOrEmpty(Login) && !string.IsNullOrEmpty(Password))
mSmtpClient.Username = Login;
mSmtpClient.Password = Password;
if (EnableSSL)
if (EnableStartTLS)
mSmtpClient.SecurityOptions = SecurityOptions.SSLExplicit;
mSmtpClient.SecurityOptions = SecurityOptions.SSLImplicit;
mSmtpClient.SecurityOptions = SecurityOptions.None;

I tried to amend the code with only using
SecurityOptions = SecurityOptions.Auto;

Attempted connection with full credential - smtp server, port, username, password, still fail to connect to the smtp server.

Attached with the Aspose smtp log for your reference.
Error stated: Smtp server: 451(LocalErrorInProcessing) 4.0.0 Error processing message.

This case happened at customer environment. Server details is not accessible outside their network.


Thank you for sharing the log file. We’re discussing it with our Product team to determine if this could be helpful in further investigating the issue. However, we may not be of much help if the error log is not of much help. We’ll be back to you on this soon with our feedback.


If you have a look at the Error 451 here: http://www.serversmtp.com/en/smtp-error, you will see that:

It’s normally a transient error due to a message overload, but it can refer also to a rejection due to a remote antispam filter. If it keeps repeating, ask your SMTP provider to check the situation. (If you’re sending a large bulk email with a free one that can be a common issue).

Please also try turning off UsePipelining i.e. StmpClient.UsePipelining = false and check if it helps.


Can you please share with us some public server where we can test the implementation of this feature? We can’t find some public email server for testing the functionality of this feature. We have found that Exchange server doesn’t support it and we can’t test it at our end.