Short answer

CDSL sends you transaction emails because it acts as your securities depository, holding and maintaining your investments on your behalf. You receive these emails as a regulatory requirement to keep you informed about all activities in your demat account. CDSL automatically sends you an email and SMS containing details of debits and credits on the T+1 day when your transactions are settled.

iRage also sends you a monthly holdings statement with details of all debits and credits in your demat account for the given month.