How warmup works

How to do it

1. Get the mailbox connected first — warmup can only be switched on for an Active mailbox, and it only runs on one with IMAP set up. Until then the Warmup tab says why ("Warmup can be turned on once this mailbox passes its connection check.", "Resume sending first…" for a paused one, or "Warmup needs IMAP to read and answer warmup mail…") and the switch stays off.
2. Flip the switch in the mailbox's Warmup column on the Mailboxes list, or open it → Warmup tab → turn on "Email Warmup", set the volume settings (see the warmup settings article) and click "Save Changes". For many at once, select them and click "Turn On Warmup". A mailbox switched on with no daily volume set (0 a day and no randomise range) starts at 20 a day, and the page says so.
3. Leave it running. Check progress on the mailbox's Overview tab, its warmup reputation in the Warmup column, and the "Warmup Network" strip on the Mailboxes page ("N warmup emails sent today · N mailboxes warming" — warming counts the active mailboxes whose warmup can run: on, with IMAP and a volume above 0).

Good to know

• Warmup never spends email credits.
• Every warmup email carries a hidden marker and your workspace's two-word code word (e.g. "Sweet-Bread"), shown on the Mailboxes page: "tag … is in every warmup email — filter on it to keep warmup out of forwarded inboxes" (Copy Tag copies it). Warmup mail is never forwarded by Reply forwarding.
• Partners are other warmup-enabled, verified mailboxes anywhere in the MailFleet network (any workspace), preferring a different domain from yours. At least 2 such mailboxes must exist for anything to send.
• A mailbox must have IMAP configured to take part — the engine needs to read its inbox to open, rescue and reply. Without IMAP its Warmup column reads "Needs IMAP to warm", it never shows as Warming, and its Warmup tab won't switch warmup on.
• The engine runs every 2 minutes. Each pass sends up to 25 warmup emails network-wide and lets up to 25 mailboxes engage; per mailbox it respects your "Warmup Emails Per Day" (hard cap 100) and the gap between its warmup sends (30 minutes by default).
• Engagement: the receiving mailbox finds the warmup email (looking back 3 days, up to 15 per pass), moves it to the Inbox if it landed in Spam/Junk ("rescued"), marks it read and flagged, and replies to a share of them according to the sender's Reply rate. Replies are threaded as "Re: <subject>".
• Subjects and bodies are composed from large pools of plain, conversational business phrases with no promotional wording, so they read as unique human notes.
• Turning warmup off is always allowed; turning it on requires the mailbox to be Active — for a paused one the switch says "Resume sending first — warmup only runs on an active mailbox.", and for one that isn't connected it's refused with "Verify this mailbox's connection before enabling warmup.". No warmup goes out from a paused mailbox, even with warmup on.
• Health jumps to 100 the first time a mailbox actually sends a warmup email (its Warmup tab then counts the days: "Day 1 · N/day today").