Email Sending Queue

Every email leaving Lumail goes through a shared sending system. Understanding it explains why a campaign takes the time it takes, and why a workflow email sometimes arrives a few minutes after the action that triggered it.

Two priority lanes

Lane	What goes in it	Priority
Instant	Transactional emails (login codes, notifications, API/SMTP single sends) and campaign test emails	Always sent first
Bulk	Campaigns and workflow emails	Sent with the remaining capacity

Whenever an instant email is waiting, bulk sending pauses until it goes out. Instant emails are rare and tiny in volume, so this pause is measured in milliseconds — but it guarantees that a password reset never sits behind a 50 000-recipient campaign.

Workflow emails are queued like campaigns

Each email step in a workflow is backed by a campaign behind the scenes. That means:

• Workflow emails use the same bulk lane as regular campaigns.
• They join the same sending queue for your organization.
• They are not prioritized over campaigns, and campaigns are not prioritized over them.

Inside one organization, the queue is first in, first out: whatever was queued first is sent first. If a large campaign starts sending at 10:00 and a subscriber triggers a workflow email at 10:01, that workflow email is sent once the campaign ahead of it has finished draining.

If you need a workflow email to go out immediately regardless of campaign volume, avoid scheduling large campaigns during the windows where that workflow is most active.

Fair share between organizations

Your queue is never blocked by another customer's campaign. Sending capacity is split across all organizations that have emails waiting:

• Half of the available capacity is reserved for paid plans.
• The rest is open to every organization, free plans included.
• Within each pool, capacity is distributed by plan weight: Business organizations get more slots than Premium, which get more than Free.
• Organizations that were short-changed in one round are prioritized in the next one, so the split evens out over time.

Practically: if you are the only organization sending, you get the full throughput. If ten organizations are sending at once, capacity is shared — and your plan determines your share.

What this means for timing

• Small campaigns and workflow emails typically leave within seconds.
• Large campaigns are delivered progressively, at a steady, deliverability-friendly rate rather than in one burst. This is intentional: sending everything at once damages sender reputation.
• Progress is visible on the campaign page while sending, so you can follow how many recipients have been processed.
• Emails are never dropped when the queue is busy — they wait, and each recipient's state is tracked individually so a retry never produces a duplicate.

When sending stops

Sending pauses for your organization in two cases:

• Monthly quota reached — campaigns are parked and workflow runs are paused. Both resume automatically at the start of the next period, or as soon as capacity frees up.
• Plan suspension — same behavior: nothing is lost, everything resumes once the account is active again.

Related Documentation

• Email Step - Send emails from a workflow
• Deliverability Score - Monitor your sender reputation
• Subscriber Events - Track delivery, opens and clicks