Vendor rate limit from shared API key
Your transactional email pipeline (password resets, receipts) starts lagging at 11:00 — emails that should send in seconds now take 20+ minutes, and some fail. Dashboards: your email vendor (SendGrid-style) API returns a rising share of HTTP 429 'rate limit exceeded' with Retry-After headers; your send queue depth is climbing steadily; your app is otherwise healthy. Recent context: at 10:45 a one-off marketing batch job started blasting a 2M-recipient newsletter through the same API key / account as your transactional mail. How do you triage and mitigate?
What a strong answer looks like
Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.
0:00 of about 30 min
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.