Replies to Approval Vote Tracking emails are processed in the listener, but do not create Email records, and do not update the vote.
The only indication of the message is when querying FRS_ops_email_incoming_queue_error, which will show the record, with simply "General Exception"
This generally occurs because there is an invalid entry in the Email Object Name Mapping workspace. Records can be seen by either opening that top level tab as an administrator, or by running the following query:
SELECT TenantEmailBONameMapping.SourceBOName, TenantEmailBONameMapping.TargetBOName, TenantEmailBONameMapping.RecId FROM TenantEmailBONameMapping
Generally, a record will exist with null values for SourceBOName and TargetBOName. Delete this entry.
If this review does not find a problematic record, the best troubleshooting process will be to perform a SQL trace during processing of the Email, and locate the following return:
exec sp_executesql N'INSERT INTO [frs_ops_email_incoming_queue_error] SELECT * FROM (SELECT [MessageLocalAutoId], [MailboxName], [MessageUID], [MessageReceivedDate], [MessageRfc822Source], [MessageProcessingStatus], [EmailSvcInstanceId], [EmailSvcLockExpirationTime], [EmailSvcLockId], [LastAccessTime], [ItsmBoType], [ItsmBoId], [Active], ''General Exception'' as [Comments] FROM [frs_ops_email_incoming_queue] WHERE [MessageLocalAutoId]=@MessageLocalAutoId) as TEMP',N'@MessageLocalAutoId int',@MessageLocalAutoId=73
Look at the queries executed prior to this for an indication of where the failure may be occurring.