What is a sender pool?
Several mailboxes sharing send volume so no single address gets flagged for sending too much.
Sender pool — A sender pool is a group of mailboxes across one or more domains that share outbound volume, so no single mailbox exceeds the daily sends that providers tolerate. It exists to protect deliverability at volumes above what one address can carry.
Also known as: mailbox pool
Why it matters
Mailbox providers throttle or block addresses that send too many messages in a day, especially cold outreach to people who have not opted in. A single mailbox can usually send a few dozen to a couple hundred messages a day before it risks its reputation. A sender pool spreads that volume across many mailboxes so each one stays comfortably under its own daily limit.
For a sales team running outbound at real volume, hundreds or thousands of contacts a week, a pool is close to mandatory; one mailbox alone cannot carry that load without damaging its reputation within days. For an agency, a separate pool per client keeps one client's sending reputation from ever affecting another's. The detail that decides whether a pool protects the business or damages it is which domain the mailboxes sit on: pooled mailboxes belong on secondary domains built for outreach, never on the company's primary domain, because a reputation hit on the pool would otherwise follow every employee's email address. In SalesCrew, pool mailboxes and their daily caps are managed as one registry, separate from the primary inbox connections used for reply handling.
How a pool is set up and used
- 1
Secondary domains are registered
Domains built for outreach, kept separate from the company's main domain.
- 2
Mailboxes are created and warmed
Each one gradually builds sending history before real outreach starts.
- 3
The mailboxes join the pool
They are grouped together with a shared daily volume budget.
- 4
Sends are distributed across them
Each message goes out from one of the pool's mailboxes, rotating to keep any one under its cap.
- 5
Bounces and complaints are tracked per mailbox
A struggling mailbox can be pulled from rotation without affecting the rest of the pool.
The mistake to watch for
Questions
- How is a sender pool different from a mailbox pool?
- They are the same thing. Sender pool and mailbox pool are used interchangeably for a group of mailboxes sharing outbound send volume to protect deliverability.
- How many mailboxes does a sender pool need?
- It depends on total volume, but a rough guide is dividing the target daily send count by the safe per-mailbox limit, typically a few dozen to a couple hundred sends a day per address, then adding a buffer of extra mailboxes for warmup and rotation.
- Should a sender pool use the company's main domain?
- No. A pool should run on secondary domains registered specifically for outreach. That way, if one of those domains takes a reputation hit from aggressive sending, the company's primary domain and every employee's email stay unaffected.