What is a sender pool and sender rotation?
Push a week of outreach through one address and its sending reputation drops long before the list runs out.
Want to see it first? Book a demo
Sender pool — A sender pool is the group of mailboxes a cold email system rotates through, picking one mailbox for each send so that no single address or domain goes over its daily cap. Sender rotation is the rule that picks the next mailbox; together they let a team send more outreach than one address can carry.
Also known as: mailbox pool, sender rotation, inbox rotation
Why rotation matters more than the pool itself
Owning twenty mailboxes doesn't protect you by itself. What protects you is how each send picks one. Rotate badly and three mailboxes carry most of the volume while the rest sit idle. Rotate well and every mailbox stays under its cap, rests between sends and drops out when it starts to bounce.
The pool is the inventory: the addresses, the sending domains they sit on and the daily budget for each. How you build that inventory, on second domains and with warmup, is covered under mailbox pool. This page is about the other half, the rotation rule that runs on every send.
For an agency, the pool is also a boundary. Each client gets its own pool, so a bad week for one client's list never touches another client's mailboxes.
Four checks a good rotation runs before each send
| Check | What it prevents |
|---|---|
| Per-mailbox daily cap | One address sending far more than the rest |
| Per-domain daily cap | Many mailboxes on one domain adding up to a spike |
| Cooldown since the last send | Bursts that look automated to the receiving server |
| Suppression at send time | Mail to someone who unsubscribed or bounced since the list was built |
How rotation picks the sender for one email
- 1
A send is due
A cadence step or campaign email is ready.
- 2
Suppression is checked
Unsubscribed or bounced? The send stops.
- 3
Eligible mailboxes are listed
Under both caps and past their cooldown.
- 4
One is chosen
The mailbox that has rested longest goes next.
- 5
The result feeds back
A bounce or complaint suppresses that contact.
The mistake to watch for
Rotation built into the CRM
SalesCrew sends cadences through a native mailbox-pool sender. It enforces per-mailbox and per-domain daily caps, stamps a cooldown on each mailbox after a send, and re-checks suppression before every email. A bounce or complaint adds the contact to suppression on its own. Read how it fits with outreach on the outbound page.
Questions
- Is a sender pool the same as a mailbox pool?
- Yes, the two names describe the same group of mailboxes. People tend to say mailbox pool when talking about setup and domains, and sender pool or sender rotation when talking about how each send is routed.
- How does sender rotation choose the next mailbox?
- It filters out mailboxes that have hit their daily cap, whose domain has hit its cap, or that sent too recently. From what's left, it picks one, often the mailbox that has rested longest. A suppression check runs before the email goes out.
- Does sender rotation replace email warmup?
- No. Warmup builds each mailbox's sending history before real outreach. Rotation keeps a warmed mailbox inside safe daily volume once outreach starts. A pool needs both.
- What happens to a mailbox that starts bouncing?
- Its bounces add those contacts to suppression, so they're never mailed again from any mailbox. If one mailbox keeps bouncing, pause it and check its domain's authentication before it returns to rotation.