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Connect Outlook and Microsoft 365.

Connect through Exchange Online client SMTP submission. The mailbox and tenant must allow SMTP AUTH, and Microsoft is moving this connection method from passwords to OAuth.

5 MIN READALL PLANSUPDATED OCT 2026

What you need.

01

A licensed Exchange Online mailbox

02

SMTP AUTH enabled for the mailbox

03

Microsoft 365 administrator access if SMTP AUTH is disabled by the tenant

04

The complete mailbox address and its current SMTP credential

Steps

  1. Turn on Authenticated SMTPSign in to the Microsoft 365 admin center. Open the user, choose Mail, then enable Authenticated SMTP.
  2. Check the tenant policyAsk your Microsoft 365 administrator to confirm that the tenant policy allows SMTP AUTH for this mailbox.
  3. Add the connection in Sync NotifyUse smtp.office365.com on port 587 with STARTTLS. Enter the complete mailbox address as the username and the credential allowed by your tenant's current SMTP AUTH policy.
  4. Test and sendRun Test and send. The From address should match the authenticated mailbox unless Exchange Online grants that mailbox Send As permission for another address.

Settings to enter.

Sync Notify fills these in when you choose the Outlook preset. They are here so you can check them.

OUTLOOK PRESET
SMTP host
smtp.office365.comExchange Online client submission
Port
587STARTTLS required; TLS 1.2 or TLS 1.3
Authentication
SMTP AUTHOAuth is preferred; password-based auth must be allowed by the tenant
Username
Full mailbox addressFor example, you@yourstore.com
Provider limits
10,000 recipients/day; 30 messages/minuteRecipient limit is 500 by default and configurable up to 1,000 per message

Common errors.

535 5.7.3Authentication unsuccessful

The mailbox credential was rejected or the tenant blocks the authentication method. Confirm the full mailbox address, reset the credential if needed, and ask the administrator to review SMTP AUTH and authentication policies.

5.7.57Client was not authenticated

Authenticated SMTP is disabled for the mailbox or organization, or the connection did not negotiate TLS. Enable Authenticated SMTP for the mailbox and use port 587 with STARTTLS and TLS 1.2 or newer.

ERR 03Messages are throttled or rejected

The mailbox exceeded Exchange Online's message-rate or recipient-rate limits. Let Sync Notify retry later, reduce the sending rate, and use a service intended for bulk email if the store needs more volume.

Official references.