Your mail service needs to either extend the time allotted for people to return to their account before wiping them clean, or to archive peoples mail accounts when they are set to be wiped clean in order to allow the individuals the opportunity to retrieve their data, which often is very important. This has been a problem for multiple people, and it is not good enough to just reinforce to yourselves that this is the policy and we will just have to conform to it. You are a service for the benefactor of the individuals that use your service, so it is of your very purpose to find ways to further improve the service that you offer.
We are people, and so are you. Please consider my words from the context of empathy and with regard to compassion.