The "Mailbox unavailable. The server response was: 5.7.1 Unable to relay" error typically occurs when you are trying to send email through a mail server that is not configured to allow relaying for your domain or IP address.
To fix this error, you need to configure the mail server to allow relaying for your domain or IP address. This will typically involve adding your domain or IP address to a list of allowed relay hosts or configuring authentication for relay access.
The specific steps required to configure the mail server will depend on the server software and configuration. If you are using a third-party email service or hosting provider, you may need to contact their support team for assistance.
Here are some general troubleshooting steps you can try:
This error message indicates that there was an issue with authenticating your email account with the SMTP server when attempting to send an email through Gmail. Here are some steps you can take to resolve the error:
Check your email account settings: Make sure that you have correctly entered your email address and password in the email client or application you are using to send the email.
Check your SMTP server settings: Ensure that you have correctly configured the SMTP server settings in your email client or application. In Gmail's SMTP settings, the server address should be smtp.gmail.com and the port should be 587. Also, make sure that the "Use SSL" or "Use TLS" option is enabled.
Check if two-factor authentication is enabled: If you have enabled two-factor authentication for your Gmail account, you may need to generate an app password to use for the SMTP server authentication instead of your regular password. To do this, go to your Google Account settings, click on "Security" and then scroll down to "App Passwords". Generate a new app password for your email client or application and use it instead of your regular password.
Check if less secure app access is enabled: If you have not enabled less secure app access in your Gmail account, you will need to do so. Go to your Google Account settings, click on "Security" and then scroll down to "Less secure app access". Turn on this option to allow your email client or application to access your Gmail account.
If none of these steps resolve the error, try logging out and then logging back into your Gmail account to refresh your login credentials. If the issue persists, contact your email client or application's support team for further assistance.
The "SMTP server requires a secure connection or the client was not authenticated" error occurs when attempting to send an email message without proper authentication or using an insecure connection.
To resolve this error, you can take the following steps:
EnableSsl property to true on your SmtpClient instance.UseDefaultCredentials property to false and supplying your username and password in the Credentials property of the SmtpClient instance.Here's an example of how you can configure your SmtpClient instance to use SSL/TLS encryption and authenticate your client:
using System.Net;
using System.Net.Mail;
// Create a new SmtpClient instance
var smtpClient = new SmtpClient("smtp.example.com", 587);
// Enable SSL/TLS encryption
smtpClient.EnableSsl = true;
// Authenticate your client
smtpClient.UseDefaultCredentials = false;
smtpClient.Credentials = new NetworkCredential("username", "password");
// Create a new MailMessage instance
var message = new MailMessage("[email protected]", "[email protected]", "Subject", "Body");
// Send the message
smtpClient.Send(message);
Note that the specific settings you need to use may vary depending on your email provider. Check with your provider for more information on how to configure your SmtpClient instance.