Problem

Using a third party smtp service provider, user reported that all emails initiated from APM were failing. When the Server Instance attempts to sent an SMTP message the following message is returned in the server log file:

021-12-14 23:08:15.3499Z Error MACHINE\User Ivara.Mail.SmtpPlugin.SmtpMessage [38] SmtpMessage::Send() - exception thrown EXCEPTION OCCURRED:SmtpException Failure sending mail.    at System.Net.Mail.SmtpClient.Send(MailMessage message)

   at Ivara.Mail.SmtpPlugin.SmtpMessage.Send(Boolean bAutoSend)

IOException Unable to read data from the transport connection: net_io_connectionclosed.   

   at System.Net.Mail.SmtpReplyReaderFactory.ProcessRead(Byte[] buffer, Int32 offset, Int32 read, Boolean readLine)

   at System.Net.Mail.SmtpReplyReaderFactory.ReadLines(SmtpReplyReader caller, Boolean oneLine)

   at System.Net.Mail.SmtpReplyReaderFactory.ReadLine(SmtpReplyReader caller)

   at System.Net.Mail.CheckCommand.Send(SmtpConnection conn, String& response)

   at System.Net.Mail.MailCommand.Send(SmtpConnection conn, Byte[] command, MailAddress from, Boolean allowUnicode)

   at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception)

   at System.Net.Mail.SmtpClient.Send(MailMessage message)

Solution

This is a generic error used for a variety of problems.  In this case, the cause was that an update to the third party SMTP Service Provider credentialsdid not persist when changed while the Server service was running.  These credentials are maintained in APM Configuration/Server Instance/Full settings/Server Email Settings.   

For this type of change, the Server Instance service must be stopped, credentials updated and saved, and then the Server service restarted.