How many cold emails should one mailbox send a day?

We cap a warmed Google mailbox at 15 cold emails a day and a warmed Microsoft mailbox at 5. Those numbers look small next to the 30 or 50 a day that older advice used to allow. We keep them small because one burned mailbox costs us more than the extra sends would have earned.

What is our daily cold email limit per mailbox?

The limit depends on the provider and on how old the mailbox is. A mailbox that has warmed for at least 30 days gets the full cap. A younger one gets a lower cap, and we never let any mailbox go to 30 a day.

Microsoft gets the lower number because its spam filters and fingerprinting are much more aggressive than Google's. We found that our old rule of up to 30 a day was too hot, so we cut it.

Why do we only load a share of the cap?

We plan steady sending at about 70% of what the attached mailboxes could send. We allow a range of 65 to 75%, and 70% is the default. The rest is room for the days when a mailbox needs to slow down or a lead load arrives late.

We also measured how our sending tool spreads the work. It spreads sends fairly evenly across mailboxes that have the same limit, so a 70% load on the whole group is close to a 70% load on each mailbox. That is why we size the caps for the group and re-run the sizing every week and after every new lead load.

One rule we keep is that we never remove a mailbox from a running campaign to create room. A lead keeps the first mailbox that emailed it, so pulling a sender breaks those threads. We would rather lower the cap.

How does a daily cap become a monthly number?

We multiply the cap by the load and by the working days in a month. For a warmed Google mailbox that is 15 emails a day, times 70%, times 22 working days. That comes to 231 emails a month from one mailbox.

A warmed Microsoft mailbox at 5 a day follows the same math. That is 5 times 70% times 22, or 77 emails a month. We use the same method on every client program, so the number is easy to check against our outbound calculator.

The monthly figure is a ceiling for planning, not a promise for every mailbox. Some Microsoft mailboxes sit on domains shared with many other mailboxes, and our sending tool's support team told us to send only 2 cold emails a day from those. When a domain holds only two mailboxes, we have run 5 a day, and we raise it only after bounces stay clean.

Why do new mailboxes need a 30-day warmup?

A fresh mailbox that starts cold sending right away damages its own deliverability and can burn the whole domain. Warmup is the slowest part of setting up any new sending system, so we plan for it first. We hold every new mailbox for a full 30 days before it joins a sending batch.

We enforce that gate at two separate points. A new domain only enters our rotation once at least one of its mailboxes is 30 days old. Any individual mailbox under 30 days is also kept out of the active sending group.

Warmup stays on for every mailbox, including the ones that are sending cold email. We do not turn it off for volume. When we raise a Google cold cap, we raise the warmup number with it, at about one and a half times the cold number.

When do our emails go out?

Every campaign sends Monday to Friday from 8:30 in the morning to 5:30 in the afternoon, Eastern time. One window for every program makes the results easier to compare and easier to audit.

The window is also the reason we count 22 working days a month and not 30. A mailbox that rests on weekends does not send on them. We break down what this volume costs to run on our infrastructure cost page.

Common questions