Who told you that e621 is halal?

There is no authoritative source that confirms e621 (monosodium glutamate) is halal or haram; its status can depend on individual interpretations within different cultures and communities. Typically, e621 is derived from fermentation processes and is considered permissible in many contexts, but it's always best to check with reliable halal certification bodies or consult with knowledgeable religious authorities for specific dietary concerns.