Catalyzes the transfer of a methyl group from dimethylamine to the corrinoid cofactor of MtbC (PubMed:10852929). The major or perhaps only DMA methyltransferase expressed under inducing conditions (PubMed:16096277). Co(I)-[dimethylamine-specific corrinoid protein] + dimethylamine + H(+) = methyl-Co(III)-[dimethylamine-specific corrinoid protein] + methylamine One-carbon metabolism; methanogenesis from dimethylamine. May form homotetramers or homopentamers. Induced by growth on trimethylamine but not methanol or monomethylamine. Part of the mtbC-mttB-mttC-mttP-mtbB1 operon. Belongs to the dimethylamine methyltransferase family.