Leadify runs a global consecutive delivery failure feature which counts failed marketing messages. When a marketing message id queued for a contact, the contact is checked against this database. If the contact has failed previously, the likelihood of failure again is high and thus this contact is excluded.
This ensures that you are not wasting your marketing budget on contacts that would likely not receive your SMS or email. Furthermore, the quality of your leads also improves, which underpins the efficacy of your entire lead-generation efforts.