Hello
I don't think there is a standard SAP housekeeping job which is run with a standard variant to cleanup the sent mails with a default retention period.
Read these SAP notes:
Note 988057 - Reorganization - Information
Note 966854 - Reorganization - New report
KBA 1641830 - Reorganization of Business Communication Services data (RSBCS_REORG)
The reports mentioned in the notes are used for deleting them and they prompt for a retention period.
As far as I know if the given reports are used then the cleaning is done else not.
Regards
RB