How to Warm Up 300 Inboxes: Cost, CSV, Domains and Private Pool

Warming up 300 inboxes costs $580/month on a new BobWork Email Warm-up account, because the first 10 mailboxes are free and the remaining 290 are billed at $2 each. Ignore the account limit, DNS and pool setup, and your upload will fail before warm-up helps. This guide gives the setup order, CSV format, ramp maths, domain spread and outbound checks.

At 300 mailboxes, warm-up is infrastructure. You need working mailbox credentials, billing active, the account limit raised above the default 200, DNS on every sending domain and a way to read fleet health without opening every inbox.

If you are still choosing a fleet size, compare this plan with the smaller and larger guides for CSV mailbox imports, warming 10+ email accounts and warming 500 mailboxes. The same rules apply, but mistakes get louder at 300.

How much does it cost to warm up 300 inboxes?

A new BobWork Email Warm-up account includes 10 active mailboxes free. At 300 active mailboxes, the monthly cost is $580. Billing is handled by Stripe, prorated and cancellable any time. Extra mailboxes pause without billing.

Early users who created accounts before 27 October 2026 keep 20 free mailboxes for as long as they use the product. At this size, that is $20 less than the new-account price.

The default account limit is 200 mailboxes. For 300 mailboxes, request a higher limit before upload by emailing info@bobwork.ai. Do this before preparing the final CSV, so you do not split the work across avoidable batches.

Do not compare only headline prices. Compare the billing unit. Some warm-up tools bill per inbox. Some bill as part of an outreach platform. BobWork bills per account, with 10 free mailboxes for new accounts and lower paid mailbox cost at larger sizes.

For broader price context, see the bulk agency warm-up guide and the cheapest way to warm up 50+ inboxes.

What must be ready before upload?

Set up the account before you prepare 300 credentials. The common failure is simple: the mailboxes are ready, but only 200 can connect.

Use this order:

1. Create the BobWork account.
2. Add billing, because 300 exceeds the free limit.
3. Email info@bobwork.ai to raise the account limit above 200.
4. Choose shared network or private pool.
5. Prepare mailbox credentials.
6. Upload a small CSV batch.
7. Fix failed rows.
8. Upload the full CSV.
9. Let each mailbox ramp on its own schedule.

BobWork runs a shared warm-up network by default. Every active mailbox on the service exchanges warm-up emails with other active mailboxes across accounts. One mailbox is enough to start in shared mode.

At 300 mailboxes, use a private pool in most cases. In private mode, only your account’s mailboxes write to each other. Nobody outside the account receives those mailbox addresses. A private pool needs at least two mailboxes, so 300 is more than enough.

Switch it in the dashboard:

Mailbox pool → Pool mode → Private pool

If you want the trade-off first, read private warm-up pools vs public networks. Shared is simpler for small accounts. Private is cleaner for large fleets.

How do you upload 300 mailboxes?

Use the bulk upload flow. In BobWork, go to:

Add mailbox → Many mailboxes: upload a CSV

Paste or upload rows with these columns:

``text email,app_password,name alex@domain1.com,abcd efgh ijkl mnop,Alex sam@domain2.com,wxyz abcd efgh ijkl,Sam ``

For Gmail, Yahoo and iCloud, BobWork fills in the host settings. For other domains, add imap_host. Each row gets the same IMAP and SMTP login test as a single mailbox connection.

Already-connected rows are skipped, so re-uploading is safe. Failed rows are listed with the reason. At 300 mailboxes, expect some credential, IMAP or provider-setting failures on the first pass.

For Gmail and Google Workspace, the recommended route is IMAP with an app password. App passwords require 2-Step Verification. Google explains the setup in Sign in with app passwords. Workspace admins may also need to allow IMAP.

BobWork also has one-click Google sign-in, but it is limited. Google caps unverified apps at 100 users, BobWork has not done the CASA audit and Google shows an unverified-app notice. For 300 Gmail or Workspace inboxes, app passwords are usually the practical route.

For Yahoo and iCloud, use app passwords. For Lark Mail, use IMAP plus a mail-client password. For Zoho Mail, use the Zoho Mail API route or IMAP on Mail Lite and above. Zoho’s free plan works through the API route.

For Amazon SES, SendGrid and Mailgun, warm-up uses the platform’s SMTP credentials for sending plus a receiving inbox over IMAP. Do not upload SMTP-only senders without a real receiving mailbox, because the engine needs to detect placement and replies.

If the fleet is all Gmail or Workspace, keep the process boring: prepare app passwords, test a small batch, fix admin settings, then upload the full CSV. The bulk Gmail accounts guide gives the Gmail-specific version.

What ramp volume should you expect?

Each mailbox ramps separately. The default schedule starts at 3 warm-up emails per day, increases by 2 per day and caps at 30 per day. The cap is editable per mailbox, up to 100.

Weekends run at 30% of normal volume. Sends are spread across 09:00–18:00 in the mailbox’s own time zone, with decisions every 15 minutes and randomness. A pair never writes to each other twice within 3 hours.

Peers on a different domain or provider are picked twice as often. That helps mixed fleets avoid overusing the same domain pairs.

These are warm-up sends, not cold emails. About 40% of received warm-up mail gets a reply. Threads end after 3 messages. The content is plain office talk: plain text, no links, no images and first-name greetings.

Do not turn the cap to 100 just because the dashboard allows it. At 300 mailboxes, the default 30/day already creates up to 9,000 warm-up sends on weekdays once ramped. More volume is not automatically safer.

During campaigns, BobWork’s recommended practice is to keep warm-up at 10–15 per day per mailbox. For real outreach, stay around 30–50 cold emails per day per mailbox. Add mailboxes instead of forcing more volume through the same sender.

If you are planning outbound volume too, read how many cold emails per day is safe and the warm-up engine behaviour. Warm-up should support sending. It should not become the biggest signal on the mailbox.

Should 300 inboxes use a private pool?

Usually, yes. The pool decision at 300 inboxes is about control.

The shared warm-up network is the default. It fits one mailbox, a small team or early testing. The live network size is shown on the dashboard. BobWork does not publish a fixed network number in blog posts, because it changes.

Private pool is optional per account. In private mode, only your own mailboxes exchange warm-up emails. Nobody outside your account receives those mailbox addresses. This is the better fit for most 300-inbox fleets.

Private pool does not mean you can ignore domain spread. If all 300 mailboxes sit on one domain, you still create a narrow pattern. Use several domains and providers where possible.

Private pool also does not guarantee inbox placement. No warm-up tool can guarantee that. It creates controlled activity, rescues warm-up messages found in spam and gives you sender-level spam-rate data.

BobWork Email Warm-up does the operational work automatically in either mode: sending, replying, moving warm-up mail out of Spam, marking it read, labelling it Warm-up and archiving it after 24 hours. Only mail carrying the engine’s hidden header is touched. Real mail is never read, moved or answered.

How many domains do you need?

For large fleets, domain spread matters as much as mailbox count. BobWork’s general recommendation for big fleets is typically 2–5 mailboxes per domain. At 300 mailboxes, that means roughly 60–150 domains.

That range is not a law. It is an operating pattern. The right number depends on provider mix, domain age, sending purpose, campaign quality and complaint risk. But 300 inboxes on a tiny number of domains is harder to manage.

Every sending domain needs DNS in place before warm-up matters.

BobWork checks SPF, DKIM and DMARC daily via DNS and shows results per domain. The DKIM selector check covers common selectors including google, zmail, default, selector1, selector2, k1, s1, mail, dkim, lark, feishu and zoho.

For setup detail, use the SPF, DKIM and DMARC guide. If you hit SPF lookup problems, use the SPF 10-lookup fix.

Google’s sender guidelines say senders should authenticate mail with SPF or DKIM, and bulk senders have stricter requirements. Google also says to keep spam rates below 0.1% and avoid ever reaching 0.3% or higher in Postmaster Tools. Read the primary source in Google’s email sender guidelines.

Yahoo’s sender best practices require SPF and DKIM, DMARC at least p=none, aligned From domains, one-click unsubscribe for bulk mail, spam rate under 0.3% and valid PTR records. Yahoo also says unsubscribes should be honoured within 2 days. See Yahoo Sender Hub best practices.

Warm-up does not replace those requirements. It gives the mailboxes a safer activity pattern while DNS, provider reputation and campaign behaviour settle.

How do you read fleet health?

At 300 mailboxes, do not inspect every inbox manually. Use fleet-level rules, then investigate outliers.

BobWork’s spam rate is sender-based. It is the share of a sender’s warm-up mail that receiving mailboxes found in Spam over the last 7 days. This is better than guessing from opens, because it is measured directly inside receiving mailboxes. BobWork does not use third-party seed lists.

The health score runs from 0 to 100:

A mailbox is ready for outbound when all three conditions are true:

1. It has warmed for at least 7 days.
2. Its 7-day spam rate is 3% or lower.
3. It has received at least 30 warm-up emails.

Use those gates across the whole fleet. Do not start all 300 senders because the oldest 20 look ready.

If a mailbox goes above 5% spam rate, pause it for a few days. Check DNS, provider warnings, password or IMAP errors, sending history and whether the domain is too concentrated.

This is where automation beats manual warm-up. With 300 inboxes, manual sending and replying becomes inconsistent. Automated warm-up keeps the schedule, reply pattern, spam rescue and archive rules consistent. The comparison is covered in manual email warm-up vs automation.

If you also send cold email from the same warmed mailboxes, keep warm-up running. BobWork’s optional Outbound feature only sends from mailboxes that passed the ready gate. New outbound mailboxes start at 30 cold emails per day for the first week after ready, then 50 per day after that.

What should you do now?

Use this checklist before you upload 300 mailboxes. It is shorter than recovery work after a bad upload.

After upload, do not judge the fleet in the first hour. You are testing credentials, access and DNS first. Warm-up results need days, because the ready gate requires at least 7 days.

For an existing domain, BobWork’s recommended practice is 7 days before cautious outbound. For a new domain, use 2–3 weeks. With 300 inboxes, new domains deserve the slower path.

The practical setup is simple: request the 300-mailbox account limit, add billing, upload the CSV, switch to a private pool and let every mailbox ramp from 3 to 30 warm-up emails per day. Start with BobWork Email Warm-up at emailwarmup.bobwork.ai, then use the dashboard health, spam rate and domain checks to decide when each sender is ready.

How much does it cost to warm up 300 inboxes?

For a new BobWork Email Warm-up account, 300 active mailboxes cost $580/month. The first 10 are free. Early users who keep their 20 free mailbox allowance pay $20 less at this size.

Can I connect 300 mailboxes at once?

Yes. Use Add mailbox → Many mailboxes: upload a CSV. The CSV uses email, app_password and name. Gmail, Yahoo and iCloud hosts are filled in automatically. Other domains need imap_host.

Do I need to raise my account limit?

Yes. The default account limit is 200 mailboxes. Ask for a higher limit at info@bobwork.ai before uploading the full 300-mailbox CSV.

Should 300 inboxes use a private pool?

Usually, yes. BobWork recommends a private pool once you have 50+ mailboxes. At 300, your own mailboxes are enough to warm each other, and nobody outside your account receives those addresses.

How many domains do I need?

A typical spread is 2–5 mailboxes per domain. For 300 mailboxes, that means about 60–150 domains. Every domain still needs SPF, DKIM and DMARC.

How much warm-up volume will 300 inboxes create?

On weekdays, 300 inboxes create up to 900 warm-up sends on day 1, 4,500 on day 7, 8,700 on day 14 and 9,000 per day once capped at 30 each. Weekends run at 30%.

Can I warm up Outlook or Microsoft 365 inboxes?

Not yet in BobWork Email Warm-up. Microsoft requires OAuth, and Outlook/Microsoft 365 support is not live. Use Gmail, Google Workspace, Zoho, Lark, Yahoo, iCloud, SES, SendGrid, Mailgun or IMAP+SMTP mailboxes instead.

Frequently asked questions