Sending and rotation
How Zylar sends campaign email: rotation across inboxes, daily caps per inbox, random gaps between sends and sending windows in each lead's time zone.
Sending is the third deliverability layer in Zylar, after setup and warm-up. Instead of sending a campaign from one inbox in a burst, Zylar spreads it across your inboxes, caps each inbox's daily volume, spaces sends with random gaps and only sends inside business hours in each lead's time zone. All four are on by default.
Rotation across inboxes
Zylar spreads each campaign across inboxes. Rather than tying a sequence to a single mailbox, it distributes sends over the inboxes available to it, so no single inbox carries the whole campaign.
Rotation only uses healthy inboxes:
- An inbox whose health score drops is switched to warm-up only (
resting), and its sends move to healthy inboxes. - A domain that is auto-paused has its volume moved to your other healthy domains.
This is why it pays to have more than one inbox and more than one domain: rotation needs somewhere to send when something is rested. See How many inboxes do you need for cold email?.
Replies always go out from the inbox that sent the original email, so a lead sees one consistent sender in the conversation. See Unibox.
Daily caps
Each inbox has a daily limit. You set it per inbox, and Zylar raises it gradually rather than all at once. An inbox won't send campaign email beyond its cap in a day.
You can read each inbox's current daily limit, along with its health score and status, with GET /inboxes in the API.
A common rule of thumb in cold email is a modest per-inbox volume, scaled by adding inboxes rather than pushing each one harder. Warm-up emails don't count toward your plan's monthly sends. See Plans and billing.
Random gaps
Zylar leaves random gaps between sends. Email sent at perfectly regular intervals is an obvious automation pattern. Randomized spacing makes sending from each inbox look more like a person working through their outbox.
Spintax in your sequence copy does the same job for content: it varies wording across sends so messages don't repeat a pattern. See Sequences.
Time-zone windows
Zylar sends in each lead's time zone, during business hours only. A lead in London and a lead in San Francisco on the same step each receive the email during their own working day, instead of one of them getting it in the middle of the night.
Out-of-office replies are handled too. When a lead's out-of-office reply includes a return date, Zylar pauses that lead and resumes the sequence the day after they're back.
How the layers work together
| Control | What it prevents |
|---|---|
| Rotation | One inbox carrying a whole campaign and burning out. |
| Daily caps, raised gradually | Sudden volume spikes from an inbox. |
| Random gaps | Machine-regular sending patterns. |
| Time-zone windows | Emails landing outside the recipient's business hours. |
| Health score and auto-pause | Continuing to send from inboxes or domains that are slipping. |
Plan infrastructure
Where your mail is sent from depends on your plan:
| Plan | Sending infrastructure |
|---|---|
| Growth | Premium shared pool |
| Scale | Premium shared pool |
| Agency | Dedicated IP pools: isolated, single-tenant sending, so other senders can't drag your reputation down |
| Enterprise | Private cluster |