Messages sent to non-owned addresses and non-owned domains are kept for a maximum of 4 days. There is a limit of 6 messages per inbox. For most customers on the Basic Plan, this will be addresses in the mailsac.com domain.
Messages may be recycled sooner in order to ensure system availability for paid customers.
For customers on paid plans, messages sent to owned addresses and owned domains will be recycled once the message storage limit for the account is reached. Oldest messages are removed first.
For additional information about message storage, recycling, and storage management see the Message Storage Documentation