Check the logs in the hostserverin folder - they may have more detail on what the error actually is.

Checked logs and pasted as following.  Thanks for any tips!

"75515712","2021-12-17 16:59:19","Error","General","24148","UMEmptyQError","K2DestQueue.RunDestQueue","24148 The User Manager 127.0.0.1 returned an empty queue with name ***********.","anonymous","0.0.0.0","sxbjoa01:D:Program FilesK2Host ServerBin","75515712","621f4c584cab4c4ea535e5904c2edae5",""
"75519880","2021-12-17 17:04:32","Error","General","0","ErrorMessage","SourceCode.Workflow.Common.SmtpMail: ","0 System.Net.Mail.SmtpException: Failure sending mail ---> System.IO.IOException: Unable to read data from the transport connection: net_io_connectionclosed。
在 System.Net.Mail.SmtpReplyReaderFactory.ProcessRead(ByteB] buffer, Int32 offset, Int32 read, Boolean readLine)
在 System.Net.Mail.SmtpReplyReaderFactory.ReadLines(SmtpReplyReader caller, Boolean oneLine)
在 System.Net.Mail.SmtpReplyReaderFactory.ReadLine(SmtpReplyReader caller)
在 System.Net.Mail.CheckCommand.Send(SmtpConnection conn, String& response)
在 System.Net.Mail.MailCommand.Send(SmtpConnection conn, Byten] command, MailAddress from, Boolean allowUnicode)
在 System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception)
在 System.Net.Mail.SmtpClient.Send(MailMessage message)
--- end of inner exception stack trace ---
在 System.Net.Mail.SmtpClient.Send(MailMessage message)
在 SourceCode.Net.Mail.SmtpConnection.Send(MailMessage message)
在 SourceCode.Workflow.Shapes.Execution.Mail.SmtpMail.SendWithSMTP(MailMessage mailMessage, K2LoggerProxy logger, String SmartObjectServerConnectionString, String smtpConnectionString)","anonymous","0.0.0.0","sxbjoa01:D:Program FilesK2Host ServerBin","75519880","3a0f18c987c944cda947aa983b3e08d3",""
"75519881","2021-12-17 17:04:32","Error","General","0","ErrorMessage","SourceCode.Workflow.Common.SmtpMail","0 SMTP mail send failure: Verify the SMTP connection strings are correct and that SMTP is working properly. Exception: Failure sending mail","anonymous","0.0.0.0","sxbjoa01:D:Program FilesK2Host ServerBin","75519881","bea13cd539a74f2aa4da95f62ce8a866",""
"75519882","2021-12-17 17:04:32","Error","General","28083","ExtenderExecuteError","ProcessInstance.HandleException","28083 ServerEvent: There is no connection string for the destination email address notify@silexmicro.com.

Server stack trace:
在 SourceCode.Workflow.Runtime.Extenders.AssemblyExtender.OnExecute(Object context, XmlElement data, ResolverManager resolverManager)
在 SourceCode.Workflow.Runtime.Extenders.ResolverExtenderBase.Execute(Object context, String data)
在 System.Runtime.Remoting.Messaging.StackBuilderSink._PrivateProcessMessage(IntPtr md, Objecte] args, Object server, Object ]& outArgs)
在 System.Runtime.Remoting.Messaging.StackBuilderSink.SyncProcessMessage(IMessage msg)

Exception rethrown at r0]:
在 System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
在 System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
在 SourceCode.Workflow.Runtime.IK2Extender.Execute(Object context, String data)
在 SourceCode.KO.ProcessInstance.ExecuteExtender(Guid A_0, State A_1, ContextType A_2, Object A_3, Int32 A_4, String A_5, Guid A_6)
InnerException: 调用的目标发生了异常。
在 System.RuntimeMethodHandle.InvokeMethod(Object target, Object ] arguments, Signature sig, Boolean constructor)
在 System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Objecte] parameters, Objectn] arguments)
在 System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object.] parameters, CultureInfo culture)
在 SourceCode.Workflow.Runtime.Extenders.AssemblyExtender.OnExecute(Object context, XmlElement data, ResolverManager resolverManager)
InnerException: There is no connection string for the destination email address notify@silexmicro.com.
在 SourceCode.Workflow.Shapes.Execution.Mail.SmtpMail.Send(MailMessage mailMessage, K2LoggerProxy logger, String SmartObjectServerConnectionString, String processInstanceIdentifier)
在 SourceCode.Workflow.Shapes.Execution.Mail.EmailItem.SendEmail(String processInstanceIdentifier)
在 SourceCode.Workflow.Shapes.Execution.Mail.EmailEventItem.Run(ServerEventContext context, IResolverContext resolver)","","","sxbjoa01:D:Program FilesK2Host ServerBin","75519882","d8d4f2c0a339433ba8118b5ff74418e9",""
"75523018","2021-12-17 17:06:41","Error","General","0","ErrorMessage","SourceCode.Workflow.Common.SmtpMail: ","0 System.Net.Mail.SmtpException: 发送邮件失败。 ---> System.IO.IOException: 无法从传输连接中读取数据: net_io_connectionclosed。
在 System.Net.Mail.SmtpReplyReaderFactory.ProcessRead(Byte�] buffer, Int32 offset, Int32 read, Boolean readLine)
在 System.Net.Mail.SmtpReplyReaderFactory.ReadLines(SmtpReplyReader caller, Boolean oneLine)
在 System.Net.Mail.SmtpReplyReaderFactory.ReadLine(SmtpReplyReader caller)
在 System.Net.Mail.CheckCommand.Send(SmtpConnection conn, String& response)
在 System.Net.Mail.MailCommand.Send(SmtpConnection conn, Bytek] command, MailAddress from, Boolean allowUnicode)
在 System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception)
在 System.Net.Mail.SmtpClient.Send(MailMessage message)
--- 内部异常堆栈跟踪的结尾 ---
在 System.Net.Mail.SmtpClient.Send(MailMessage message)
在 SourceCode.Net.Mail.SmtpConnection.Send(MailMessage message)
在 SourceCode.Workflow.Shapes.Execution.Mail.SmtpMail.SendWithSMTP(MailMessage mailMessage, K2LoggerProxy logger, String SmartObjectServerConnectionString, String smtpConnectionString)","anonymous","0.0.0.0","sxbjoa01:D:Program FilesK2Host ServerBin","75523018","43c20bb802aa481588db3abdcc88363b",""
"75523019","2021-12-17 17:06:41","Error","General","0","ErrorMessage","SourceCode.Workflow.Common.SmtpMail","0 SMTP mail send failure: Verify the SMTP connection strings are correct and that SMTP is working properly. Exception: 发送邮件失败。","anonymous","0.0.0.0","sxbjoa01:D:Program FilesK2Host ServerBin","75523019","56be9b683f72480183020af267db8705",""
"75523020","2021-12-17 17:06:41","Error","General","28083","ExtenderExecuteError","ProcessInstance.HandleException","28083 ServerEvent: There is no connection string for the destination email address notify@silexmicro.com.

Server stack trace:
在 SourceCode.Workflow.Runtime.Extenders.AssemblyExtender.OnExecute(Object context, XmlElement data, ResolverManager resolverManager)
在 SourceCode.Workflow.Runtime.Extenders.ResolverExtenderBase.Execute(Object context, String data)
在 System.Runtime.Remoting.Messaging.StackBuilderSink._PrivateProcessMessage(IntPtr md, ObjectR] args, Object server, Objectn]& outArgs)
在 System.Runtime.Remoting.Messaging.StackBuilderSink.SyncProcessMessage(IMessage msg)

Exception rethrown at a0]:
在 System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
在 System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
在 SourceCode.Workflow.Runtime.IK2Extender.Execute(Object context, String data)
在 SourceCode.KO.ProcessInstance.ExecuteExtender(Guid A_0, State A_1, ContextType A_2, Object A_3, Int32 A_4, String A_5, Guid A_6)
InnerException: 调用的目标发生了异常。
在 System.RuntimeMethodHandle.InvokeMethod(Object target, Objectr] arguments, Signature sig, Boolean constructor)
在 System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object�] parameters, Objecte] arguments)
在 System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object.] parameters, CultureInfo culture)
在 SourceCode.Workflow.Runtime.Extenders.AssemblyExtender.OnExecute(Object context, XmlElement data, ResolverManager resolverManager)
InnerException: There is no connection string for the destination email address notify@silexmicro.com.
在 SourceCode.Workflow.Shapes.Execution.Mail.SmtpMail.Send(MailMessage mailMessage, K2LoggerProxy logger, String SmartObjectServerConnectionString, String processInstanceIdentifier)
在 SourceCode.Workflow.Shapes.Execution.Mail.EmailItem.SendEmail(String processInstanceIdentifier)
在 SourceCode.Workflow.Shapes.Execution.Mail.EmailEventItem.Run(ServerEventContext context, IResolverContext resolver)","","","sxbjoa01:D:Program FilesK2Host ServerBin","75523020","d8c7798279a24ecba40c976f92495606",""
"75523941","2021-12-17 17:07:17","Error","General","0","ErrorMessage","SourceCode.Workflow.Common.SmtpMail: ","0 System.Net.Mail.SmtpException: 发送邮件失败。 ---> System.IO.IOException: 无法从传输连接中读取数据: net_io_connectionclosed。