This is only a tip for those who don’t know this yet.
There is an ABAP program called SSF_ALERT_CERTEXPIRE that can be used to check if digital certificates will expire soon (not only for NF-e application). For example, you can schedule a SSF_ALERT_CERTEXPIRE job to run every day and send you an email alerting that a certificate will expire in the next 60 or 30 days so you can plan the renewal and don’t have unexpected issues due to expired certificates.
For more information please check SAP Note ‘572035 – Warning about expired security certificates‘ and pay attention to the details on how to run it! 🙂