Cannot send mail through SQL Server sp_send_dbmail. Certificate error

Below is the error message I see in windows event log. No errors while executing sp_send_dbmail 1) Exception Information =================== Exception Type: Microsoft.SqlServer.Management.SqlIMail.Server.Common.BaseException Message: There was an error on the connection. Reason: A connection was successfully established with the server, but then an error occurred during the login process. (provider: SSL Provider, error: 0 - The certificate chain was issued by an authority that is not trusted.), connection parameters: Server Name: LAM90DB01, Database Name: msdb Data: System.Collections.ListDictionaryInternal TargetSite: Void OpenConnection(Microsoft.SqlServer.Management.Common.SqlConnectionInfo) HelpLink: NULL Source: DatabaseMailEngine HResult: -2146232832 StackTrace Information =================== at Microsoft.SqlServer.Management.SqlIMail.Server.DataAccess.ConnectionManager.OpenConnection(SqlConnectionInfo connectionInfo) at Microsoft.SqlServer.Management.SqlIMail.IMailProcess.QueueItemProcesser.ProcessQueueItems(String dbName, String dbServerName, Int32 lifetimeMinimumSec, LogLevel loggingLevel, Byte[] encryptionKey, Int32 connectionTimeout) Exception Type: System.ComponentModel.Win32Exception NativeErrorCode: -2146893019 ErrorCode: -2147467259 Message: The certificate chain was issued by an authority that is not trusted Data: System.Collections.ListDictionaryInternal TargetSite: NULL HelpLink: NULL Source: NULL HResult: -2147467259