Inner membrane component of the type II secretion system required for the energy-dependent secretion of extracellular factors such as proteases and toxins from the periplasm. Plays a role in the complex assembly and recruits EpsL resulting in a stable complex in the inner membrane. Provides thus a link between the energy-providing EpsE protein in the cytoplasm and the rest of the T2SS machinery. Type II secretion system is composed of four main components: the outer membrane complex, the inner membrane complex, the cytoplasmic secretion ATPase and the periplasm-spanning pseudopilus (By similarity). Forms homodimers (PubMed:15081815, PubMed:17921296). Interacts with EpsL/GspL (PubMed:10322014, PubMed:10633109). Interacts with EpsE/GspE (PubMed:10633109). Interacts with EpsF/GspF (PubMed:10633109). The periplasmic region found in the proximity of the transmembrane appears to be critical for a stable interaction with EpsL. Absence of EpsM results in a decreased amount of EpsL in type II secretion system complexes. Belongs to the GSP M family. Truncated N-terminus.