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Overview

TenantCore does not connect to Instantly directly. The integration happens at the mailbox level — you retrieve credentials from TenantCore and enter them into Instantly as email accounts.

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Prerequisites

  • At least one mailbox provisioned in TenantCore with a Verified domain status
  • An Instantly account with available email account slots

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Step 1 — Retrieve Mailbox credentials from TenantCore

  1. Open the TenantCore app and navigate to the Mailboxes page
  2. Find the mailbox you want to connect
  3. Copy the credentials

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Step 2 — Add the email account in Instantly

  1. In Instantly, go to Accounts
  2. Click Add Account and select Outlook or Microsoft 365
  3. Sign in with your Outlook credentials and click Accept when asked for permissions. This utilizes secure OAuth.
  4. Once the status shows Connected, your mailbox is ready for warm-up or campaigns.

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Step 3 — Configure send limits in Instantly

Set your Instantly per-account send limit at or below the limit enforced in TenantCore. If Instantly attempts to exceed the TenantCore limit, Exchange will block the excess messages and Instantly may log delivery errors.
In Instantly, open the account settings and configure:
  • Daily email limit — match this to the TenantCore mailbox limit or set it lower
  • Sending window — spread sends across business hours; avoid scheduling bursts
The TenantCore limit is the hard ceiling. Instantly’s limit controls scheduling. Keeping them aligned avoids NDRs and error flags in Instantly’s account health dashboard.

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Repeat for each mailbox

Add each TenantCore mailbox as a separate account in Instantly. Use Instantly’s account grouping or tagging to keep client mailboxes organized if you are managing multiple clients.

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Troubleshooting

Connection fails
  • Confirm the mailbox password was copied correctly — passwords are case-sensitive
  • Confirm the domain shows as Verified in TenantCore before attempting to connect
  • Confirm the mailbox status is Active in TenantCore
Delivery errors after connecting
  • If messages are being blocked, the Instantly send limit likely exceeds the TenantCore mailbox limit
  • Reduce Instantly’s daily email limit to match or fall below the TenantCore limit