How Many Cold Emails Should One Mailbox Send per Day?

The number

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

Treat 25 as a ceiling, not a target. Running below it per mailbox and getting volume from more mailboxes is the safer way to scale.

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.

How to ramp a new mailbox

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 instead of sending them in one batch.

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.

• Warm-up 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

Add mailboxes, not per-mailbox volume. Each new mailbox needs its own warm-up, so plan capacity three 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.

What we recommend at Outreach2day

Up to 25 cold emails per mailbox a day, not counting warm-up, up to 5 mailboxes per domain, warm-up for at least 14 days before cold email, full volume around day 21, and warm-up kept running while you send. The send 100,000 cold emails a month guide walks through the full setup.