Before going into the details about MMID, one should first understand about IMPS.
What is IMPS?
‘IMPS’ means Immediate Payment Service in the context of the Indian banking system. Just like National Electronic Fund Transfer (NEFT) and RTGS (Real-time gross settlement), IMPS is a money transfer mechanism. However, unlike NEFT and RTGS, the IMPS system works on bank off-days and holidays too as it is available 24 x 7.
‘IMPS’ is managed by the National Payments Corporation of India (NPCI). The Reserve Bank of India (RBI) and NPCI envisioned the IMPS system as a 24 by 7 fund transfer mechanism. To achieve this, they made the system compatible to both online and mobile banking platforms. When users transfer money through IMPS using mobile banking, Mobile Money Identifier (MMID) is used to verify and secure the transaction.

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What is MMID?
MMID or Mobile Money Identifier is a unique seven digit code issued by a bank to their mobile banking registered-customers who want to transact through the IMPS fund transfer platform. The first four digits in an MMID code are the distinct ID no. of the bank offering IMPS services. Since IMPS is an immediate, real-time, inter-bank fund transfer mechanism which is enabled through electronic means, safety measures such as MMID are required to keep the transactions secure.