Most teams clean reactively.
They wait until:
- bounce rates climb
- an ESP warns them
- inbox placement weakens
- a major campaign underperforms
That is the expensive version of the lesson.
Better moments to clean
The best time is usually before one of these:
- a major campaign
- an ESP migration
- a large import from another source
- a reactivation send after a long pause
- the next quarterly maintenance window
Why timing matters
Cleaning before the send means the bad addresses never get the chance to become bounce data, reputation damage, or noisy reporting.
That is much easier than recovering after the fact.
A simple rule
If the list has aged, changed, or grown since the last review, it is probably worth another cleanup pass before the next important send.