You should never use the casual term "domo" in formal professional settings, high-stakes business negotiations, official corporate correspondence, or when addressing corporate superiors, clients, teachers, or elderly individuals. Because domo is an informal conversational shorthand, using it in hierarchical or formal environments signals a lack of respect, poor manners, and unprofessionalism. Additionally, you should strictly avoid using "domo" when offering a serious apology; while it can occasionally soften a minor acknowledgment, apologizing for a significant mistake requires formal expressions like moshiwake arimasen or sumimasen deshita. In Japan's heavily stratified social and professional etiquette, defaulting to polite, complete honorific language (keigo) in formal contexts prevents misunderstandings and demonstrates that you understand and respect proper cultural boundaries and mutual hierarchy.