How should I structure auto-refill for a steady monthly send volume?

For a Valid Email Checker account doing steady monthly verification volume — a SaaS doing signup-form verification, an ESP cleaning lists regularly, an agency running monthly campaigns for clients — the right structure is a Monthly plan plus auto-refill, sized to absorb spikes without ever surprising you with a downtime moment.

Step 1: pick a Monthly plan that covers normal volume

Look at the last 90 days of verification volume. Take the median month, not the peak. The Monthly tier you pick should give you slightly more than the median — say 110 to 120% of the median month. The two-bucket credit system uses monthly credits first, so anything within your normal envelope is covered by the Monthly grant alone. See PAYG vs Monthly for the underlying mechanics and why monthly credits get used before PAYG.

Step 2: set auto-refill threshold at 10 to 15% of the Monthly grant

Auto-refill fires when your combined balance drops below the threshold. Setting it at 10 to 15% of your Monthly grant gives you headroom before the refill triggers (you don't refill on every small dip) while keeping a buffer in case a spike eats through the rest of the monthly bucket faster than the next billing cycle catches up.

Step 3: pick a refill PAYG tier sized for one typical spike

When auto-refill fires, it adds a PAYG tier you select in advance. Pick a tier large enough to cover a single bad-spike day — usually 25 to 50% of your monthly Monthly grant. Going smaller means refill fires too often. Going larger means the first refill of a quiet month over-buys credits that sit untouched (though PAYG never expires, so the downside is moderate).

Step 4: choose Balanced timing

Auto-refill has three timing modes:

• Aggressive (immediate) — refill fires the moment your balance drops below threshold. Good for accounts where downtime is unacceptable, but you'll occasionally double-fire if a brief dip recovers on its own.
• Balanced (5-minute delay) — refill fires only if the balance has been below threshold for 5 minutes. This filters out transient dips and is the right choice for almost everyone.
• Scheduled — refill fires only at specific times you configure. Useful for accounting reasons (predictable monthly invoice timing) but rarely worth the complexity.

For a steady-volume account, Balanced is right. See the auto-refill setup guide for the full UI walkthrough.

Step 5: set a monthly auto-refill limit

The auto-refill modal has a 'maximum refills per month' setting. Default it to a number that covers a worst-case month — 3 to 5 refills is plenty for a normal account. The cap prevents a runaway loop (buggy integration calling the API in a tight loop) from billing you for thousands of dollars overnight. Hitting the cap pauses refill until you intervene; you'll see a notification in the dashboard.

Step 6: monitor the first 60 days

Watch Credits History for the first two billing cycles. If auto-refill fires more than once or twice per month, your Monthly tier is undersized — upgrade. If it never fires at all, your Monthly tier is too large — downgrade. Settling in usually takes one or two cycles.