VBForums - C# https://www.vbforums.com/ This forum is for all C# questions. en Sun, 19 Jul 2026 07:58:59 GMT vBulletin 60 https://www.vbforums.com/images/misc/rss.png VBForums - C# https://www.vbforums.com/ <![CDATA[[RESOLVED] C# application getting error using SMTP for one user who got a new computer]]> https://www.vbforums.com/showthread.php?912101-RESOLVED-C-application-getting-error-using-SMTP-for-one-user-who-got-a-new-computer&goto=newpost Tue, 23 Jun 2026 13:23:06 GMT Status Code: Mailbox unavailable. Code: --------- // 06/22/26 - Code from google search of "c# SmtpClient message unable to send to all recipients". catch (SmtpFailedRecipientsException ex) { // Loops through only the specific recipients that failed foreach (SmtpFailedRecipientException innerEx in ex.InnerExceptions) { //Console.WriteLine($"Failed recipient: {innerEx.FailedRecipient}"); //Console.WriteLine($"SMTP Status Code: {innerEx.StatusCode}"); MessageBox.Show(String.Format("Failed Recipient: {0} Status Code: {1}", innerEx.FailedRecipient, innerEx.StatusCode)); } } --------- The mailbox should not be unavailable. Another user sent it fine. So I don't think it's my code, I think it's the user's "new computer". Does anybody know of something that needs to be set up/configured to be able to do this? What about the new computer is relevant: OS, programs installed, etc.? I think I can fix the problem by taking the 5 or so people who are in the group and adding them one at a time to the MailMessage.To list, but that won't really help us know what this problem is and I would like to know that. Thank you for any insight.]]> There is a function in my application where a user creates an Excel file and sends it as an attachment to a group email, let's call it salessupport@vbforums.com, using SMTP. A user who has always been able to do this successfully until yesterday is getting this exception. I wrote this block of code yesterday to catch SmtpFailedRecipientsException when I was getting a very general exception "Unable to send to all recipients". This message is not much better. It says Failed Recipient: <salessupport@vbforums.com> Status Code: Mailbox unavailable.

Code:
                        // 06/22/26 - Code from google search of "c# SmtpClient message unable to send to all recipients".
                        catch (SmtpFailedRecipientsException ex)
                        {
                            // Loops through only the specific recipients that failed
                            foreach (SmtpFailedRecipientException innerEx in ex.InnerExceptions)
                            {
                                //Console.WriteLine($"Failed recipient: {innerEx.FailedRecipient}");
                                //Console.WriteLine($"SMTP Status Code: {innerEx.StatusCode}");
                                MessageBox.Show(String.Format("Failed Recipient: {0} Status Code: {1}", innerEx.FailedRecipient, innerEx.StatusCode));
                            }
                        }
The mailbox should not be unavailable. Another user sent it fine. So I don't think it's my code, I think it's the user's "new computer". Does anybody know of something that needs to be set up/configured to be able to do this? What about the new computer is relevant: OS, programs installed, etc.? I think I can fix the problem by taking the 5 or so people who are in the group and adding them one at a time to the MailMessage.To list, but that won't really help us know what this problem is and I would like to know that. Thank you for any insight. ]]> C# MMock https://www.vbforums.com/showthread.php?912101-RESOLVED-C-application-getting-error-using-SMTP-for-one-user-who-got-a-new-computer