How Many Cold Emails Should One Mailbox Send per Day?

The number

Up to 25 cold emails per mailbox per day. Warmup emails don't count toward it: they run alongside, on top of the 25.

Treat 25 as a ceiling. Running below it per mailbox and getting volume from more mailboxes is the safer way to scale.

Per domain: up to 125 cold emails a day

That is up to 5 mailboxes on one domain at up to 25 cold emails each. Warmup emails run on top and do not count. Gmail tracks volume per domain as well as per mailbox, so to send more, add domains and mailboxes and keep each one at its limit. Mailboxes are $2.50 a month with warmup included.

Why the number is this low

You will still see advice of 50 or 100 emails a day for a warmed account. We recommend 25 because above that, mailboxes and domains burn out sooner.

Providers also track volume above the mailbox. Google's sender guidelines say Gmail "tracks volume, feedback, and limits per domain and IP address." DKIM and SPF quotas are specific to your domain, while "The IP address quota is shared for all senders that use that IP address." So the per-mailbox number is one of three limits: per mailbox, per domain and per sending IP.

When a new mailbox can send

Google's advice for anyone increasing volume points the same way: "Send email at a consistent rate. Avoid sending email in bursts," and "Start with a low sending volume to engaged users, and slowly increase the volume over time."

Spread each mailbox's sends across the working day.

Signs you are sending too much

• 421 4.7.28 deferrals from Gmail for an unusual rate of email. See the 4.7.28 error.

• Temporary 4.7.500-699 "Access denied, please try again later" errors from Microsoft 365.

• Warmup spam rate rising on mailboxes that recently went up in volume.

• All campaigns dropping together right after total volume went up.

Google's SMTP error reference describes 4.7.28 as "Gmail has detected an unusual rate of email." Google's guidelines say to reduce volume when messages start bouncing or being deferred, and to increase slowly again once errors fall.

How to send more

Scale by adding mailboxes, with per-mailbox volume unchanged. Each new mailbox needs its own warmup, so plan capacity two weeks ahead. For example, 1,000 emails a day is 40 mailboxes at 25 each, on 8 domains with 5 mailboxes per domain. See how many mailboxes you need and mailboxes per domain.

Raise total volume in steps and watch each step for a few days before the next one.

Vendors set their own numbers, and they differ a lot. Maildoso caps cold email at 15 per mailbox a day (Maildoso review), ScaledMail allows 25 on Google mailboxes and 10 on Outlook and SMTP (ScaledMail review), Premium Inboxes recommends no more than 15 (Premium Inboxes review), and MailDeck gives 4 to 5 for its Outlook inboxes on the pricing page and 10 in its help docs (MailDeck review). Size your mailbox count on your vendor's own number; the cold email cost calculator shows what Maildoso's 15-a-day cap does to the mailbox count and the monthly cost at the same volume.

Questions

How many mailboxes and domains do I need for 2,000 cold emails a day?

80 mailboxes on 16 domains: 2,000 divided by 25 cold emails per mailbox is 80 mailboxes, and at up to 5 mailboxes per domain that is 16 domains. Each new mailbox needs 14 days of warmup before its first cold email, so set them up two weeks ahead. For any other volume, the cold email capacity calculator does the same math and adds spare mailboxes.

What we recommend at Outreach2day

Up to 25 cold emails per mailbox a day, excluding warmup, up to 5 mailboxes per domain, warmup for 14 days before cold email, full volume from day 14, and warmup kept running while you send. The send 100,000 cold emails a month guide walks through the full setup. Other providers state their own daily limits, from 15 to 50; the providers are compared in best cold email infrastructure providers.