Warmup, Cold email, Deliverability
Can You Use a Separate Warmup Tool Alongside Instantly or Smartlead? What Their Docs Say (2026)
Instantly and Smartlead both warm your mailboxes for you. You can still use an external warmup tool with the mailboxes they send from, as long as only one warmup runs on each mailbox. Here is what their official documentation says, and how to set it up safely.
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In this article
- Instantly's official email warmup feature: what the documentation says
- Smartlead's official email warmup feature: what the documentation says
- Can you run an external warmup tool alongside Instantly or Smartlead?
- The risks of running two warmups on one mailbox
- How to use a separate warmup tool with Instantly or Smartlead safely
- Using Warmerly next to Instantly or Smartlead
- Frequently asked questions
Yes, you can use a separate warmup tool alongside Instantly or Smartlead: the mailbox belongs to you, and any tool that connects to it can warm it while Instantly or Smartlead sends your campaigns. Neither vendor's help center, as of October 13, 2026, addresses running a second warmup tool on the same mailbox. Our advice is to run one warmup per mailbox: pause the built-in warmup first, then turn on the external one, and keep total daily volume inside the limits both vendors' docs recommend.
We make Warmerly, a warmup and outreach tool that can run next to Instantly or Smartlead, so we have a stake in this answer. Everything attributed to Instantly or Smartlead below comes from their own help articles (help.instantly.ai and helpcenter.smartlead.ai), read on October 13, 2026. Where the docs are silent, we say so and label our own recommendation.
Instantly's official email warmup feature: what the documentation says
- How it works: your account joins a pool of other Instantly users with warmup switched on. Warmup emails are opened automatically, many get replies, and any that land in spam are moved to the inbox.
- How long: Instantly says an account should be warmed for at least 2 weeks before campaigns, and that its health score (the share of warmup emails reaching the inbox over seven days) should be above 90%. That score covers warmup mail only, not campaign mail.
- Default settings: a daily warmup limit of 10 is suggested for new accounts, rising by 1 a day, with a 30% reply rate. Instantly asks you not to enable Disable slow warmup on new accounts.
- Filtering: a warmup filter tag keeps warmup emails out of your primary inbox. You can keep the default tag, change it, or generate a random one.
- Pools: the status icon shows whether an account is paused or in a basic, standard, or premium and private pool. Warmup can be disabled if your account bounces warmup emails from other users, and then needs a reactivation code.
Smartlead's official email warmup feature: what the documentation says
- How it works: enabling warmup adds the mailbox to a shared pool. Smartlead sends warmup emails to other users, and handles opening, spam rescue and replies; your mailbox also receives warmup emails from other users.
- Identification: warmup emails carry a custom identifier tag that you set in the warmup settings, and Smartlead has a separate guide to its warmup filters.
- Volume during campaigns: if the mailbox is in an active campaign, Smartlead recommends keeping total daily warmup emails at 10 to 20, and raising them once the campaign finishes. Its auto-adjust option lowers the warmup count by 7 to 10 while the mailbox is in a live campaign.
- Ramp-up: daily ramp-up is for fresh domains. Smartlead says it is not needed if the domain is already warmed or you are coming from another warmup engine.
- Reply rate: 20 to 30% is recommended, and above 30% is not advised unless you are an expert.
- Sending limits: warmup emails do not count toward the mailbox's daily sending limit in Smartlead. Bounce protection takes accounts out of the pool when bounces occur.
| Instantly | Smartlead | |
|---|---|---|
| Warmup network | Pool of other Instantly users | Shared pool of Smartlead users |
| Suggested daily warmup for a new account | 10, rising by 1 a day | Ramp-up on for fresh domains; 10 to 20 a day during a live campaign |
| Suggested reply rate | 30% for new accounts | 20 to 30% |
| How warmup mail is identified | Warmup filter tag | Custom identifier tag |
| Minimum warmup before campaigns | At least 2 weeks, health score above 90% | Not stated in the warmup setup articles; its troubleshooting guide says warmup typically takes 2 to 6 weeks |
| Says anything on third-party warmup tools? | No | Only that ramp-up is not needed when coming from another warmup engine |
Can you run an external warmup tool alongside Instantly or Smartlead?
Yes, in the sense that matters: Instantly or Smartlead sends your campaigns, and a different tool warms the same mailbox. Smartlead's docs expect people to arrive from another warmup engine, which is the same situation in reverse. What neither help center covers is running both warmups on one mailbox at the same time, so there is no vendor guidance that says it is allowed or forbidden.
Our recommendation, which is ours and not either vendor's: never warm one mailbox in two networks at once. Pick the built-in warmup or the external one per mailbox. People usually switch to an external tool because they want placement tests, DNS monitoring, or warmup that stays put if they change sending tools.
The risks of running two warmups on one mailbox
- Double volume. Both tools ramp independently. Instantly suggests 10 a day for a new account and Smartlead 10 to 20 during a live campaign; two networks each following their own curve can push a young mailbox well past either figure, on top of your campaign sends.
- Conflicting tags and filters. Each tool identifies its own warmup mail with its own tag. Mail from the other network does not match, so it can land in your real inbox, get mixed up with prospect replies, or be sorted by rules meant for something else.
- Misleading health numbers. Instantly's health score only measures its own warmup mail. With a second network in play, neither tool's score tells you where your campaign mail lands.
- Stacked reply rates. Two tools each replying at 20 to 30% creates a pattern that neither vendor's settings were designed around.
- Harder diagnosis. If placement drops, you cannot tell which network, or which setting, caused it.
How to use a separate warmup tool with Instantly or Smartlead safely
- Pause the built-in warmup for the mailbox. In Instantly, click the flame icon on the account or use Bulk pause warmup on the Email Accounts page. In Smartlead, switch warmup off in the account's warmup settings.
- Connect the same mailbox to the external tool, and leave that tool's own campaign sending off so Instantly or Smartlead remains the only sender.
- Choose a ramp that matches the mailbox's history. A mailbox that is already warm does not need to start again from one email a day, which matches Smartlead's own advice on ramp-up.
- Keep campaign volume steady during the change, and keep total daily volume in a safe range: about 40 to 50 cold emails a day for a warmed mailbox.
- Check for leftover filters or labels from the old warmup and remove any that would hide real mail.
- Run an inbox placement test after the first week, since the old tool's health score no longer reflects the mailbox.
Using Warmerly next to Instantly or Smartlead
Warmerly can warm a mailbox while Instantly or Smartlead keeps sending, with Warmerly's own campaigns left unused. It also checks SPF, DKIM and DMARC daily and runs inbox placement tests. The free plan covers one mailbox with no card; Starter is $19 a month for 5 mailboxes. Be honest with yourself about whether you need it: if Instantly's or Smartlead's warmup is working and your placement is fine, a second tool is a cost without a benefit.
Frequently asked questions
Does Instantly have built-in email warmup?
Yes. Instantly's help center says connected accounts join a warmup pool of other Instantly users, where warmup emails are opened, replied to and moved out of spam. It suggests at least 2 weeks of warmup and a health score above 90% before using an account in campaigns.
Does Smartlead have built-in email warmup?
Yes. Smartlead's help center says enabling warmup adds a mailbox to a shared pool, where warmup emails are sent, opened, rescued from spam and replied to. It recommends 10 to 20 warmup emails a day while the mailbox is in an active campaign.
Can I use a different warmup tool with Instantly or Smartlead?
Yes. Instantly or Smartlead can send campaigns while another tool warms the same mailbox. Neither vendor's help center covers running two warmups on one mailbox at once, so pause the built-in warmup before turning on the external one.
Is it bad to run two warmup tools on the same mailbox?
It is not advisable. Two networks ramp independently and can double warmup volume, each tool's filter tag only catches its own mail, and neither tool's health score then reflects reality. Run one warmup per mailbox.
Do I lose my warmup progress if I switch warmup tools?
No. Sender reputation belongs to your domain and mailbox at Gmail and Microsoft, not to the warmup tool. Smartlead's own docs say daily ramp-up is not needed when you come from another warmup engine.