A link that is an auto notification could be allowed to expire in 30 days if the portal maintains a reference inventory of listings that were sent. This allows for the cleaning of old links yet allows for the maintaining of the information history if the client pops back into activity. A link to either stored information, a reference report, or a listing that is manually created and sent should be preserved and should die with the portal/client.
Also consider changing the paradigm so that a client will only receive one link to their portal and within the portal is all information. This creates only one link per client/portal into perpetuity of the life of that purchasing/selling cycle.
Either the 1st choice or let the agent select one of the methods. Dormant leads can pop back up and I don't want my MLS system to arbitrarily clean the list. Thanks.