Methods and systems for multimedia messaging service (MMS) authentication over IP networks are disclosed. An access identifier records message corresponding to a user by a multimedia messaging service center (MMSC) forwarded by a server is received. Data from the access identifier records message including a mobile directory number, a framed IP address, access network information and a session ID is extracted and stored in a cache accessible to the MMSC. Network IP authentication is executed to determine that the user has a valid IP address. Client IP authentication of the user is executed to determine that the valid IP address is stored in the cache. A correspondence between the valid IP address and a mobile directory number of the user is determined. The user is authenticated for MMS over the IP network based on the correspondence.