Im getting an error when a client is trying to authenticate. THe message is below. I replaced the ip addresses with *

Anyone know what this means

cmd: STARTTLS
[2022.03.03] 12:56:20.443 [*.*.*.*][43119453] rsp: 220 Start TLS negotiation
[2022.03.03] 12:56:20.458 [*.*.*.*][43119453] rsp: 554 Security failure
[2022.03.03] 12:56:20.458 [*.*.*.*][43119453] Exception negotiating TLS session: System.Security.Authentication.AuthenticationException: A call to SSPI failed, see inner exception. ---> System.ComponentModel.Win32Exception: The certificate chain was issued by an authority that is not trusted
[2022.03.03]    --- End of inner exception stack trace ---   at System.Net.Security.SslState.StartSendAuthResetSignal(ProtocolToken message, AsyncProtocolRequest asyncRequest, Exception exception)   at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)   at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)   at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)   at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)   at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)   at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)   at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest)   at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)   at MailService.TcpServerLib.Common.PooledTcpItem.ConvertToSSL(db_system_binding_port setting, Log log, String sessionId)   at MailService.TcpServerLib.SMTP.SMTPSession.STARTTLS()12:56:20.458 [*.*.*.*][43119453] disconnected at 3/3/2022 12:56:20 PM