If an email is auto-imported from a known contact but their latest job is in the Completed stage, the message will remain unassigned and appear in your 'No Job Assignment' sidebar list. A common case of this is a former client (with a completed job) emailing about booking you for a new job.
Emails Between Táve Users
Emails sent between two Táve users outside of Táve will not auto-import. While the two employees may be discussing something relevant to a job in Táve, they could also be discussing confidential information (i.e. salary, inter-office politics, juicy gossip), and therefore it wouldn't be appropriate to import those into a system shared by multiple employees. To import messages between two employees relevant to a job, simply assign the 'Import to Táve' label to the email in Gmail.