If your Outlook or Microsoft 365 mailbox shows a health error or fails to connect in GetReplies, the most common cause is that SMTP authentication (Authenticated SMTP) is disabled for your mailbox or your entire Microsoft 365 tenant. GetReplies uses SMTP/IMAP to send and receive emails, so this must be explicitly enabled.
The error you will typically see
535 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Tenant.
This means SMTP auth is turned off at either the tenant level or per-mailbox level in your Microsoft 365 admin.
How to enable SMTP Auth for a specific mailbox
You (or your IT admin) need to do this for each mailbox you want to connect to GetReplies:
Go to the Microsoft 365 Admin Center.
Navigate to Users → Active users.
Click on the user whose mailbox you want to enable.
In the flyout panel, click the Mail tab.
Click Manage email apps.
Check the box for Authenticated SMTP.
Click Save changes.
Repeat this step for each mailbox you are adding to GetReplies.
Also ensure IMAP is enabled
While in the Manage email apps panel, also check that IMAP is enabled. GetReplies needs both SMTP (to send) and IMAP (to receive and track replies) to function correctly.
Set up DKIM for your sending domain
For best email deliverability, also enable DKIM for your domain in the Microsoft 365 Defender portal:
Go to security.microsoft.com.
Navigate to Email & Collaboration → Policies & Rules → Threat Policies → DKIM.
Select your domain and toggle DKIM signing to Enabled.
Use a secondary domain for outreach mailboxes
GetReplies recommends using mailboxes on a secondary domain (e.g. yourcompany-outreach.com) rather than your primary business domain for outreach campaigns. This protects your main domain's sender reputation. Set up domain forwarding on the secondary domain to redirect to your main website.
After enabling SMTP — reconnect in GetReplies
Go to Accounts in the left menu.
Delete the mailbox that was showing an error.
Click Add Account → select Outlook / Microsoft 365.
Enter your email address and password, then click Connect.