A boundary becomes easier to understand when it describes what you will do. ‘Stop expecting me to reply all the time’ expresses frustration, but it leaves the actual arrangement unclear.
Try: ‘I usually check personal messages after work. If I haven’t replied during the day, it doesn’t mean I’ve missed the conversation permanently.’ This gives the other person useful information about your availability.
For a repeated work issue, you might say: ‘I can review requests received by four. Anything later will go into the next working day unless we agree otherwise.’ Make sure that arrangement fits your actual role and obligations.
A boundary is different from a demand that someone feel or behave exactly as you want. You can explain when you will respond; you cannot guarantee that another person will never be disappointed.
Keep the wording proportionate and avoid attaching an unrelated punishment. If there is a practical consequence, state it plainly and follow through consistently.
Before sending, ask whether the recipient can describe the boundary in one sentence. They should know the behaviour, the limit and any relevant exception. Clear boundaries can reduce guessing while preserving room for a respectful conversation about what each person needs.