How Many Emails Per Day Per Mailbox Is Safe

Why no one can give you one number

A sending limit is a provider policy, and providers differ: shared hosting caps a mailbox per hour, a dedicated server has no application limit but the receiving side still has opinions, and a bought SMTP account sits somewhere in between. On top of the provider cap sits the reputation of the domain and the address the mail leaves from.

Receivers add the practical ceiling. A new domain sending a thousand messages on day one is the pattern of a spam run, so a share of those messages is throttled, filtered or rejected regardless of what your provider allows. That is why the same mailbox can send 200 a day happily and cause problems at 2,000.

Sizing a pool from your target

Start with the monthly volume and divide by working days. Ten thousand a month over 20 sending days is 500 a day. At 100 a day per warmed mailbox that is five mailboxes; at 50 a day, ten. Build the pool with headroom, because a mailbox that is at its limit every day has no room for a retry.

Then check the arithmetic against your bounce rate. A pool sized for 500 a day and a list with 5 percent invalid addresses spends 25 of those sends on bounces, and bounce rate is the metric that most often triggers a provider review. Clean the list, then size the pool.

• Monthly volume divided by sending days gives daily volume.
• Daily volume divided by the per-mailbox rate gives the pool size.
• Add 20 to 30 percent headroom for retries and uneven load.
• Hold new mailboxes at the low end for the first two weeks.
• Recheck the pool when you add a second sending domain.

What a provider actually watches

Volume is only one signal. Providers suspend on complaint rate, bounce rate, blocklist appearances and sudden changes in pattern, such as a mailbox that sent ten a day for a month and then 800. The abrupt change matters more than the absolute number.

That is why the schedule should be gradual even when the plan is aggressive. Ramp by a fixed percentage each day, keep the same sending window, and keep the content broadly similar so a sudden change in what you send does not coincide with a change in how much.

Worked example: a 30,000-message launch that stalled on day three

A small agency had 30,000 contacts for a product launch and bought ten mailboxes, planning 1,500 sends a day each. Every mailbox was new, on one new domain. Day one delivered, day two delivered less, and by day three the provider had suspended the whole pool with a bounce rate near nine percent from a list that had never been verified.

Rebuilding took three weeks. The list was verified first, which removed about a fifth of the addresses. Two mailboxes were warmed for fourteen days on genuine one-to-one volume, then raised gradually to 150 a day each. The launch went out over six weeks in segments instead of four days, and the complaint rate stayed under the threshold that had triggered the review.

The arithmetic at the end was unglamorous: 24,000 valid addresses, two mailboxes at 150 a day for 20 days a month, 6,000 messages a month, four months of sending. That is what the plan should have been from the start, and the only number in it that came from outside was the provider's cap.

Sizing a pool from a monthly target

The rates are planning figures for a warmed mailbox on a domain with authentication in place, not a provider promise. A new domain should start well below them.

Set the limit from evidence, not a forum post

• 1Convert the monthly target into a daily figure over 20 sending days.
• 2Confirm what your provider caps per mailbox per hour as well as per day.
• 3Check SPF, DKIM and DMARC are passing before you plan any volume.
• 4Warm each new mailbox from a low start over two weeks.
• 5Watch bounce and complaint rates weekly and slow down before a suspension, not after.