How a warmup pool works, seen from inside your mailbox

In short

• A warmup pool is a set of real mailboxes that exchange short messages. The service reads, answers and files them automatically.
• The service acts inside your mailbox: it searches the inbox and the spam folder, marks messages as read, moves pool mail out of spam and replies.
• An app password or IMAP login reaches the whole mailbox. What a tool does with your other mail depends on what it commits to in writing.
• Other members of the pool see your email address and display name.
• Before joining, ask who is in the pool, how large it is compared with your volume, what it reports and how you leave. WarmupBay's pool is new and its size is not published.

A warmup pool is the group of mailboxes that a warmup service lets write to each other. Your mailbox sends a few short messages a day to other members. The service then signs in to the receiving mailbox, opens the message, answers some of them, and moves a message to the inbox if it landed in spam. The pool decides who you exchange mail with, and the access you grant decides what the service can do in your mailbox.

What a pool is, and what it is not

The members of a pool are mostly the mailboxes of other customers. Instantly's help center puts it this way: "When you enable warmup, your account joins a pool of other Instantly users who have also enabled the feature." Some services add mailboxes of their own. Warmerly's network terms (24 September 2026) say that the participating mailboxes "include other customers' mailboxes and may include mailboxes that we host or operate ourselves".

The mail is real. It leaves through your own provider, and it passes the spam filter of the partner's provider like any other message. That is why the result means something: when a warmup message lands in a Gmail spam folder, Gmail's filter put it there.

A pool is not a placement test. In a placement test you send one of your real messages to a list of test addresses to see where it lands. Some tools offer both. They answer different questions.

One exchange, step by step

1. The service picks a partner. You do not choose. Warmerly's terms state it openly: "We decide which mailboxes exchange mail with each other, how much each mailbox sends and receives, when, and what the messages say."
2. Your mailbox sends a short message. The service signs in with the access you gave it and sends through your provider, as a mail program would.
3. The partner's provider files it. Inbox, a tab such as Promotions, or spam. This is the one step nobody in the pool controls.
4. The service signs in to the partner's mailbox and looks for the message, in the inbox and in the spam folder.
5. It acts on the message. It marks it as read, moves it out of spam if needed, and usually files it in a folder or under a label.
6. For some messages, the partner's mailbox replies. The reply goes through the same steps in the other direction.
7. The service records where the message landed. That record is what your dashboard shows.

The volume is small and grows slowly. As an example with real numbers, this is WarmupBay's schedule: 3 warmup emails on the first day, one more each day, until the daily limit is reached.

How the tool tells warmup mail from your real mail

A service has to find its own messages among everything else in a mailbox. Vendors describe different ways of doing that (all read on 5 October 2026):

• An ID in the message, plus a filter you set up. Warmup Inbox writes in its help article: "All these emails contain your unique ID". It suggests you "create a folder and set up a filtering rule for them". lemwarm's setup guide likewise tells you to "create a filter in your email provider".
• The identifiers of the messages it sent. Warmerly's terms: "The warmup automation identifies warmup mail by the message identifiers of the messages it sent, and acts only on those messages."
• A folder of its own. WarmupBay files warmup mail in a folder called "WarmupBay".

This is worth asking about. It decides whether pool mail clutters your inbox, and how precisely the service can keep to its own messages.

What the tool does inside your mailbox

The list is longer than "sends a few emails". These are the actions vendors themselves name:

WarmupBay sends short messages to other mailboxes in the pool, replies to some of the warmup mail it receives, takes warmup mail out of the spam folder and files it in the "WarmupBay" folder. The full list is shown in the connect flow, before you enter a password.

Two side effects are easy to miss.

Other members see your address. Pool mail is real mail, so every partner receives your email address and display name. Warmerly's terms spell this out: the address and display name "are visible to the other participating mailboxes it exchanges mail with, because that is how the network functions". This is true of every pool, ours included. Do not enrol a mailbox whose address you want to keep private.

People who share the mailbox will notice. Short friendly messages from strangers, in a folder nobody remembers creating: that is the pool. Tell colleagues who read the same mailbox before one of them marks the messages as spam.

What access you hand over

A warmup service signs in to your mailbox in one of two ways. In practice both reach the whole mailbox.

With a password of some kind. For Gmail and Google Workspace that is an app password. Google's help page describes it as "a 16-digit passcode that gives a less secure app or device permission to access your Google Account". At a hosting provider it is the mailbox password, used over IMAP (the protocol for reading mail) and SMTP (the protocol for sending it). There is no version of this access that covers only one folder.

Through the provider's sign-in screen (OAuth). Here the provider lists the permissions an app asks for. For Gmail over IMAP that is still the whole mailbox: Google's documentation says "The scope for IMAP, POP, and SMTP access is https://mail.google.com/."

So the limit on what a tool does with the rest of your mail is not technical. It is what the tool commits to in writing. Look for a sentence like the one in Warmerly's terms: "It does not open, move or reply to your other mail." If a tool says nothing about your other mail, ask.

WarmupBay is no exception. It connects Gmail and Google Workspace with an app password and other providers over IMAP and SMTP, so the access covers the whole mailbox. The connect flow lists what the service does in your mailbox, including what happens with mail that is not warmup mail. Read that step, and do not connect if it is more than you want to grant.

Taking access back is simple. Delete the app password in your Google account, or change the mailbox password at your host. Google also notes: "we revoke your app passwords when you change your Google Account password". Google itself does not recommend app passwords. What that means for warmup is covered in Is email warmup allowed?

Standard, premium and private pools

Some services run more than one pool and place you by plan or by track record. A few examples from their own documentation, as of 5 October 2026:

• Instantly describes a Premium Warmup Pool of "high-quality, aged Google and Microsoft accounts", with access that starts "at $500/month per workspace". It also offers a private pool: "Fully isolated warmup environment - only your accounts are used", from $1,000 a month.
• Smartlead lists four pools, from Foundation to Ultra Premium, tied to the plan and to criteria such as account age, authentication, bounce rate and reply rate.
• Snov.io offers a premium sender pool "to warm up with business email addresses only, not regular @gmail or @outlook accounts".

The common thread is that vendors treat the make-up of a pool as the thing that matters. A private pool is the far end of that idea: only your own mailboxes, writing to each other.

WarmupBay has one shared pool and no tiers.

Who else is in the bay? Eight questions to ask

1. Who is in the pool? Customers only, or also mailboxes the vendor runs? At which providers? If your recipients use Gmail and Outlook, placement at small hosts tells you little.
2. How large is it compared with your daily volume? In a small pool the same few mailboxes write to each other again and again.
3. How do mailboxes get in, and what gets them removed? Warmup Inbox, for example, describes a "testing environment" of about an hour before a new inbox joins its network. Warmerly's terms list reasons for removal, such as a mailbox that is blocklisted or "damages other participants' placement".
4. What exactly does the tool do in my mailbox? Look for a written list, not a general promise.
5. What do other members see of me? At least your address and display name.
6. What does it report? Counts by provider and folder are easy to check. A composite score needs explaining. lemwarm's guide does that for its own score: "A score of 80 is not an 80% inbox rate."
7. How do I leave, and what stays behind? Messages already delivered stay in the mailboxes they reached. Warmerly's terms say so directly: "We do not recall or delete it".
8. Who carries the risk with my provider? You do. See what Google and Microsoft have put in writing.

What a pool cannot do

Pool members are not your audience. Google's sender guidelines tell senders to start "with a low sending volume to engaged users", meaning people who want the mail. A pool gives a mailbox a history of small, regular exchanges. It does not show a provider that your actual recipients welcome your messages, and neither Google nor Microsoft has published how much weight pool mail carries.

The vendors say this themselves. Warmerly: "Warmup cannot fix problems caused by poor lists, content, authentication or sending practices." Smartlead's help page asks whether a higher pool will guarantee inbox placement, and answers "No."

WarmupBay's pool, plainly

• One shared pool. Member mailboxes exchange short messages automatically. There is no premium or private pool.
• It is new. WarmupBay started in October 2026, and we do not publish a pool size. A new pool has had little time to grow, so question two applies to us as well.
• Small volumes. 10 warmup emails a day for free. Up to 30 a day while a badge is visible in the footer of your website. No credit card, no subscription, no paid plan.
• One mailbox per account.
• Microsoft mailboxes cannot be connected yet. Gmail and Google Workspace connect with an app password, other providers over IMAP and SMTP. Microsoft 365 and Outlook.com do not work so far.
• Counts, not a score. The dashboard shows emails per day and where they landed (inbox, Gmail tab, spam), split by Google and other providers. It shows an inbox rate only once there are 20 deliveries to base it on.
• No placement tests and no blacklist monitoring.

Another tool fits better if you need to warm several mailboxes at once, if your mailbox is at Microsoft, or if you want placement tests or a private pool. Our overview of free email warmup tools lists what others offer. If one mailbox and a slow, free start is what you need, you can join the pool. The free limits and the feature list are on the home page.

Questions people ask

Do I have to answer warmup emails myself?

No. The service reads and answers them for you. Warmup Inbox, for example, tells its users there is no need to reply manually. With WarmupBay the messages are filed in the WarmupBay folder, and you can leave them there.

Can I delete warmup emails or mark them as spam?

Marking pool mail as spam works against the other members. Some terms forbid it outright: Warmerly's list reporting warmup mail as spam, blocking its senders and deleting it among the things you must not do while a mailbox is enrolled. Check your tool's rules before you tidy up.

Is a bigger pool always better?

Size helps because your mailbox meets more distinct partners. It says nothing about who those partners are. Vendors that sell premium pools point to the make-up instead, for example pools made only of Google and Microsoft accounts.

What happens when I leave a pool?

The service stops sending from your mailbox. Messages that were already delivered stay where they are, and a few replies may still arrive for a short time. Then remove the access you gave: delete the app password or change the mailbox password.

Can I run a pool with only my own mailboxes?

Yes. Some vendors sell private pools, and there are open-source tools for the same purpose. Every exchange then happens between mailboxes and domains you control, so no outside mailbox is involved.

Why does my mailbox contain short emails from people I do not know?

If the mailbox is connected to a warmup service, these are pool messages from other members. They are generated automatically and need no action from you. If nobody on your team connected the mailbox, check which apps and app passwords have access to the account and remove what you do not recognise.

Sources

1. Warmup Network Participation Terms – Warmerly
2. How Warm-Up Works and Why it's Important – Instantly Help Center
3. Premium & Private Warmup Pool – Instantly Help Center
4. How does email warmup work, and what to expect after you connect your first inbox – Warmup Inbox Help
5. How to set up and use lemwarm – lemlist Help Center
6. Understand Your Warmup Pool and Upgrade Eligibility – Smartlead Help Center
7. How to warm up your email for cold outreach – Snov.io Knowledge Base
8. Sign in with app passwords – Google Account Help
9. OAuth 2.0 mechanism for IMAP, POP and SMTP – Google for Developers
10. Email sender guidelines – Gmail Help