Email warmup that builds real sending reputation
New mailboxes and new domains start with no reputation. Warmup earns it the only way that works — real emails to real inboxes that engage back — before your first prospect ever sees a message.
What warmup actually does
Mailbox providers decide where to put your email based on how recipients have treated mail from that address and domain so far. A brand-new mailbox has no history, so its first cold emails are judged on nothing but the content and the sending pattern — and cold email content is exactly what filters are trained on.
Warmup builds that history deliberately. The mailbox sends ordinary messages to inboxes that are known to be warmed, and those inboxes open them, pull them out of spam when they land there, mark them important and reply to a share of them. To Gmail, Outlook and the rest, this looks like a real correspondent people want to hear from — because it is.
Gmail's own sender guidelines say to "start with a low sending volume to engaged users, and slowly increase the volume over time." Warmup is how you have engaged users on day one.
How MailFleet's warmup works
A network, not a pool of dummy accounts. Your mailboxes exchange mail with other MailFleet customers' warmed mailboxes — never with your leads, never with throwaway accounts. Every customer's senders both send warmup and engage with warmup they receive: opening, rescuing from spam to the inbox, flagging and replying. More real mailboxes in the network means more realistic behaviour for yours.
Tagged so it never gets in your way. Every warmup email carries your workspace's two-word code word (for example Sweet-Bread), so warmup never appears in your reply queue and, if you forward your inbox elsewhere, one filter hides it.
Tunable, per mailbox or in bulk. Bulk Edit's defaults are 20 warmup emails a day, a 30-minute minimum gap, and a 30% reply rate, and a mailbox switched on with no volume set starts at 20 a day. You can set a daily ramp-up so volume grows gradually, an inbound-reply cap, and a randomisation range so daily counts never look mechanical. Volume is capped at 100 warmup emails a day per mailbox. Warmup reads and answers mail over IMAP, so a mailbox needs its IMAP details to take part — one connected without them is marked "Needs IMAP to warm" on the Mailboxes page.
Free, on every plan, for every mailbox. Warmup sends never count against your plan's email credits or against a mailbox's daily sending limit. Connect two hundred mailboxes; warm two hundred mailboxes.
Health you can see. Each mailbox shows a health score; it jumps to 100 once its first warmup send goes out and drops if connection or sending failures accumulate. Filter the Mailboxes page by Warmup (On, Ramping Up, Off) and Health (90 – 100, 75 – 89, Under 75), turn warmup on for any selection in one click, or bulk-edit its settings.
See where it lands. The Mailboxes list shows each mailbox's warmup reputation — of its warmup emails from the last 14 days that receiving inboxes processed, the share found in the inbox rather than rescued from spam. A mailbox's own page breaks down 7, 14 or 30 days: sent, landed in inbox, saved from spam and replied, day by day. Nothing is estimated; before any warmup is processed it says so.
A sensible warmup schedule
The exact numbers depend on the provider and the age of the domain, but a pattern that consistently works:
| Week | Warmup / day | Cold sends / day | Notes |
|---|---|---|---|
| 1 | 10–20 | 0 | New domain or mailbox: warmup only. Check SPF, DKIM and DMARC pass first. |
| 2 | 20–30 | 5–10 | Begin cold sends to your best-fit, most likely-to-reply prospects. |
| 3 | 20–30 | 15–20 | Watch bounce rate (keep it under 2%) and any spam-folder placement. |
| 4+ | 20 (steady) | 20–30 | Hold warmup on permanently at a steady level; don't switch it off once you're "warm". |
MailFleet's defaults land inside this pattern: new mailboxes start at 30 messages a day with a 20-minute gap, and a campaign admits 100 new leads a day, so a mailbox never jumps from silence to volume. The ramp-up setting in warmup does the week-one-to-week-four growth for you.
Warmup is necessary, not sufficient
Warmup cannot fix a missing DKIM record, a purchased list full of dead addresses, or copy that reads like a template. Pair it with:
- Authentication — SPF and DKIM on every sending domain, DMARC if you send 5,000 or more messages a day to Gmail. MailFleet shows all three per domain and blocks a deploy while SPF or DKIM is missing. See SPF, DKIM and DMARC for cold email.
- Volume discipline — how many cold emails per mailbox per day explains why 20–30 is the ceiling that keeps working.
- Clean lists — hard bounces stop a lead's sequence automatically and a rising bounce rate pauses the campaign, but the cheaper fix is not to import dead addresses.
- Plain text — MailFleet campaigns default to plain text with tracking off, which is the format a person's email actually has.
Connect and warm in five minutes
- Go to Mailboxes → Import CSV and upload a CSV (a Smartlead export, or
Email, SMTP Username, SMTP Password). Google mailboxes use a 16-character app password. Each row is verified over SMTP and IMAP as it's added. - Select the new mailboxes and click Turn On Warmup (each keeps its own settings; one with no volume set starts at 20 a day) — or open Bulk Edit → Warmup, switch the section to Overwrite and turn warmup on to set volume, gap, reply rate and ramp for all of them at once.
- Under Bulk Edit → General, confirm the daily sending limit (30 by default) and gap (20 minutes).
- Leave it a week before the first cold campaign. The Warmup folder in Replies shows the mailbox-to-mailbox traffic if you want to watch it work.
FAQ
Is email warmup free in MailFleet?
Yes, on every plan and for every connected mailbox. Warmup traffic never counts against email credits or daily sending limits.
How long should I warm up a new mailbox before cold emailing?
At least a week of warmup-only sending for a new mailbox on an established domain; two to three weeks for a brand-new domain. Then keep warmup running at a steady level alongside cold sends.
Will warmup emails show up as replies?
No. Every warmup message is tagged with your workspace code word and kept out of the reply queue. If you forward your inbox to another address, filter on that code word.
Does warmup use my leads?
Never. Warmup runs only between MailFleet customers' own warmed mailboxes.
How many warmup emails per day is safe?
MailFleet defaults to 20 a day per mailbox and caps at 100. Most mailboxes never need more than 20–30 once warm.