How to Pick a Small Test Batch From a Big Email List (Mixed Mailbox Types)

To pick a test batch, group the addresses by mailbox type from the domain after the @, then take one address from each group in turn until the batch is full. The test-send sample picker does this in your browser: you give the sample size, it spreads the pick across Gmail, Microsoft, Yahoo, iCloud, Proton, other personal mailboxes and company domains, and the same list and seed always give the same rows.

A small first batch is a way to look before you send the rest.

Why not the first rows

A list is often sorted by source, date or company, so its first rows are one kind of address. A first batch of only company domains tells you nothing about how Gmail or Outlook treat your mail. A mixed batch lets you watch bounces and replies by type before the rest goes out. For how fast to ramp, see the email warm-up schedule and the bounce budget per inbox.

Step 1: do it by hand

Sort the list by the domain after the @, scan for the big groups, and copy a few rows from each into a new file. Doing this on a long list is slow, and picking by eye is biased towards the rows you see first. It is also not repeatable: you cannot rebuild the same batch next week.

Step 2: use the picker

1. Upload the CSV or .xlsx, or paste the cells with the header row first.
2. Pick the email column and the number of rows for the first batch.
3. Choose to spread across mailbox types or across every domain, and optionally cap each group.
4. Check the table of groups and download the sample.

How types are decided

Only by the domain after the @. Gmail and Googlemail are Gmail. Outlook, Hotmail, Live and MSN are Microsoft. Yahoo and its sister domains are Yahoo. AOL, iCloud (including me.com and mac.com) and Proton have their own groups, other known free mail domains are other personal mailboxes, and everything else is a company domain.

A company address hosted on Google Workspace or Microsoft 365 shows as a company domain, because only an MX lookup shows who hosts the mail. To split by host, use the ESP matching list splitter.

How the batch is filled

Groups are ordered from largest to smallest and the tool takes one random address from each in turn, round and round, until the batch is full or the groups are empty. A group limit stops one group filling the batch, and a seed makes the picks repeatable. Choose every domain on its own and each company domain becomes its own group. Repeated addresses count once. For a plain random sample with an invalid-rate estimate, use the email list sampler.

What this cannot do

• Mailbox types come from the domain name only, not from where the mail is hosted.
• A sample shows what happened to those addresses and predicts nothing about the rest.
• A repeatable random pick is not a statistical sample of the whole list.
• Only the first sheet of a workbook is read.

Verify before the first batch goes out

A mixed batch is still wasted if the addresses are dead. Upload the list on the verify page: the first 100 email checks are free with a Google sign-in, no card. Each address comes back valid, risky or invalid with a reason, and nothing is sent to anyone on the list. For larger or recurring lists, see bulk email verification, list cleaning and pricing.

Pick your batch now

Upload the list to the test-send sample picker.