How to delete SQL Server Database Mail history WITHOUT stored procedures
One idea could be:


script out CREATE TABLE for sysmail_attachments, sysmail_send_retries, sysmail_mailitems, and sysmail_log
start a transaction
drop the tables in that order
create the tables again using the script from 1.
commit the transaction
create a job that purges those tables regularly (like, once an hour, from the sounds of it), also in that order