Mailbox provisioning

Mailbox provisioning turns sending capacity into a reputation decision. Plan the domain, create a real mailbox, authenticate it, connect user access, and warm it while monitoring delivery signals. Warmup is one input into sender reputation. Authentication, recipient expectations, complaints, content, infrastructure, and sending history affect it.¹ A warmup tool cannot replace permission, list hygiene, authentication, or provider compliance.² Gmail, Yahoo, and Microsoft do not publish a universal 28-day mailbox schedule, so use a fixed calendar to plan the work.³

Plan the domain and mailbox count

Choose the domain structure before creating mailboxes. The count should follow the sending plan and the risk you are willing to place on each domain.

Start with one email account per domain.⁴ Adding more accounts raises the domain's overall email volume and the likelihood of blacklisting by mailbox providers.⁵ One planning method divides the daily send target by 50 for the inbox count and by 100 for the domain count.⁶

Use multiple domains and inboxes with rotation when the sending plan requires more capacity, since this approach is presented as a way to protect sender reputation and scale safely.⁷ Another framework presents three inboxes per domain as a way to manage the tradeoffs of scaling cold email.⁸ Test that option against your capacity plan and monitoring while keeping the per-domain starting point conservative.

Before creating anything, answer these questions:

• What daily send target must the mailbox plan support?
• How many domains will carry that volume?
• Which domain will handle cold outreach, and which domain will carry normal business email?
• What signal will make you pause expansion?

Create the mailbox and connect access

Email setup

Configuring and verifying

Creating email addresses

Managing email sending

Parts of email setup:

• Configuring and verifying
• Creating email addresses
• Managing email sending

Create the account on the chosen domain and verify that the mailbox works before adding it to an outreach workflow. The result should be a usable sending identity with the access and settings its user needs.

Arrange for a live mailbox to run from the new domain before sending outreach.⁹ A complete email setup includes configuring and verifying the domain, creating email addresses, and managing email sending and receiving settings.¹⁰

If an account attribute cannot be set during creation, create the account first and then modify it. Record which settings must be applied after the mailbox exists.¹¹ This keeps a mailbox from appearing provisioned while a required setting remains unset.

If you connect Office365 mail to Outreach, an Office365 administrator must complete the documented setup steps.¹² The administrator can select the applicable account or use the "Use Another Account" option to add or create one.¹³ After a successful connection, individuals with an Outreach license can connect their Office365 mail accounts to their Outreach account.¹⁴

Test sign-in, sending, receiving, and the connection used by the outreach workflow before moving on. Fix access problems while the mailbox is still unused.

Authenticate the domain

Domain records

MX

DKIM

SPF

DMARC

Parts of domain records:

• MX
• DKIM
• SPF
• DMARC

Finish the technical identity work before warmup begins. The mailbox needs working credentials and domain records that tell receiving systems how to assess its mail.

Configure MX, DKIM, SPF, and DMARC correctly before sending any cold email.¹⁵ For mail sent to personal Gmail accounts, all senders need SPF or DKIM.¹⁶ New domains need warming in the same way that new IPs do.¹⁷

Check each record at the domain level, then send a controlled test and confirm that the mailbox can receive replies. Move on only when the domain and mailbox agree on who is allowed to send.

Run the warmup phase

Start this phase after the mailbox is live and authenticated. Warmup establishes sending history gradually from a new or inactive setup.¹⁸

Warm every new inbox for at least three weeks before live campaigns begin.¹⁹ During that period, send wanted messages consistently, increase volume slowly, and monitor bounces, deferrals, complaints, and reputation, reducing volume when those signals worsen.²⁰

Treat the three-week recommendation as a planning floor, not proof that the mailbox will reach the inbox. Read the signals from the actual sending environment and keep the live launch behind them.

Move into live sending

Launch when the mailbox has passed its access and authentication checks and its warmup signals are stable. Keep the first live increase small enough to see what changed before adding more volume.

Watch the sending domain as well as the individual mailbox. A flagged sending domain can harm future transactional and personal emails alongside cold email.²¹ If performance changes, inspect the mailbox count and rotation before changing copy or targeting.²²

Record the domain, mailbox, user access, authentication status, warmup start, and live-send decision for each account. This lets you isolate a problem without changing every mailbox at once.

What not to do

Keep these mistakes out of the provisioning runbook.

• Do not send cold email from the main company domain, since it can work for one or two months before reply rates dip, sales team's one-to-one emails land in spam, and domain reputation becomes difficult to undo.^{23, 24}
• Do not treat automated warmup networks as provider-certified or as a promise of inbox placement.²⁵
• When reply rates collapse, audit mailbox count and rotation before changing the message.²²
• Do not let a single mailbox send too many emails too quickly, because providers can interpret that behavior as spam.²⁶