Yes Jmail should use the Hive to store its data.
But
It should use L2 transactions not the L1 transactions.
Hive should be a place where laws n rules should be equal for every single user.
If our lovely Dapps like @ecency @peakd @hive.blog put restrictions for regular users not to submit posts repeatedly in short time frames to protect spam then when Jmail will do such repeated transactions n even allowed then obviously Jmail will go above laws. If Jmail is allowed to send repeated L1 post transactions then obviously all our lovely dapps should allow regular users to do repeated L1 post operations in short time frames.