Say the boundary in operational terms
Name the contact, behavior, topic, access, or commitment you will and will not participate in. For a message about how to follow up before a job offer deadline, use this factual base: restate the role, conversation, submission, or promise and include the relevant date or reference.
Define any necessary exception
If an exception is necessary, give it one purpose, one channel, and a clear limit. Ask one answerable question, make any real deadline visible, and offer an easy way to close the loop. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Respond to escalation safely
Do not send daily reminders, manufacture competing offers, or contact unrelated employees for leverage. Use the official application or accessibility channel when the matter involves protected information or accommodation. You do not need the other person to agree with a boundary for you to follow it consistently.