How sending works behind the scenes
What MailFleet does every couple of minutes for a Sending campaign: who is due, which sender is used, what stops a person, and what holds an email back.
Where: Automatic — visible through Campaign → Emails (Scheduled), the lead panel on the Leads tab, and Analytics.
How to do it
- Deploy the campaign and keep it inside its sending window; the engine runs every 2 minutes.
- Watch Emails → Scheduled for what's due next and when it will actually leave.
- Open a lead from the Leads tab to see their next step, due time and last activity.
Good to know
- Each pass looks only at Sending campaigns inside their window, then at leads whose next step is due, oldest first, giving every campaign a fair share of the batch when campaigns share senders.
- A sender is chosen from your workspace's active senders with daily capacity left, allowed by the campaign's Mailboxes setting and not still inside its send gap; one email per sender at a time. Follow-ups stay with the mailbox that emailed the person before.
- Before sending: the lead is skipped for the day if the campaign's new-leads cap is reached (first email only); skipped permanently on that step if a built-in variable is empty without a fallback; and stopped everywhere if their address is on your blocklist. Workspaces on a trial with no email credits left have their sends held until topped up.
- Each email carries a unique Message-ID so replies and bounces are matched back to the exact send, the List-Unsubscribe headers, and — when on — the unsubscribe line, open pixel and tracked links. When the mailbox has a BCC to CRM address, the same email is copied to it, unseen by the lead.
- After a successful send the lead becomes Contacted (first email) and their next step is scheduled after that step's wait in days. When the last step is sent the lead is Finished.
- A reply marks the person Replied and stops them in every active campaign. "Not interested" or "unsubscribe" marks them Unsubscribed in every campaign. An out-of-office reply with a return date holds their next step and any open task until that day.
- A hard bounce marks the lead Bounced and stops them. A temporary failure is retried on the next pass. A provider saying the mailbox's daily limit is reached rests that mailbox until tomorrow.
- If a pass is interrupted after an email left but before the lead was advanced, the next pass catches the lead up without sending the same step twice.
- When no lead is still active, the campaign is marked Finished automatically. Subsequences never auto-finish — waiting for triggers is their normal state.