Outlook SMTP Error Fixed in Google Workspace: Outbound Restriction + App Password Solution (Real Case Guide)

While configuring a Google Workspace email account in Microsoft Outlook, users may encounter the error:

“The outgoing (SMTP) server doesn’t recognize your account. Please check your email address and try again.”

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This error can persist even after correct IMAP/SMTP settings, proper DNS configuration, and successful login attempts.

This article presents a real-world troubleshooting case and explains the exact root cause and final working solution.

⚙️ Environment Details

• Platform: Google Workspace (Gmail)
• Email Client: Microsoft Outlook (multiple versions tested)
• Protocol: IMAP / POP + SMTP
• Security: 2-Step Verification Enabled
• App Password: Generated and used

❌ Problem Description

• Outlook fails during account setup
• SMTP error appears consistently
• Issue persists across:
  • Multiple systems
  • Different networks
  • Various Outlook versions
• Same email works perfectly in Mozilla Thunderbird

? Initial Checks (All Correct)

The following configurations were already verified:

✔ IMAP enabled
✔ POP enabled
✔ Correct SMTP settings (465 / 587 tested)
✔ SPF, DKIM, DMARC properly configured
✔ App Password generated
✔ Google OAuth login tested
✔ Credential Manager cleared

? Despite all this, Outlook continued to fail.

? Root Cause Analysis

The issue was caused by a combination of two critical factors:

1️⃣ Google Workspace Outbound Restriction Policy

In Admin Console:

? Gmail → Routing → Restrict Delivery

A rule was active:

Allow outbound mail only to specific domains

Initially, only external domains (e.g., banking domains) were allowed.

❌ This caused:

• SMTP validation failure in Outlook
• Misleading authentication error

2️⃣ SMTP Authentication Method

• ❌ Normal Google password → Failed
• ✅ App Password → Required

Google blocks basic authentication using regular passwords for SMTP when enhanced security is enabled.

✅ Final Working Solution

After troubleshooting, the issue was resolved with the following configuration:

✔ Step 1: Update Outbound Routing Rule

In Google Admin Console:

? Add your domain to allowed list:

• sas-associates.co.in ✅

This ensured:

• Outlook SMTP test emails (self or domain-based) are allowed

✔ Step 2: Use App Password in Outlook

Instead of normal password:

• Generate App Password
• Use it in Outlook configuration

✔ Step 3: Correct SMTP Settings

Incoming (IMAP)

• Server: imap.gmail.com
• Port: 993
• Encryption: SSL/TLS

Outgoing (SMTP)

• Server: smtp.gmail.com
• Port: 587
• Encryption: STARTTLS
• Authentication: Enabled

? Why This Fix Works

⚠️ Important Technical Insight

Outlook performs an SMTP validation test during setup:

• Sends test email
• If domain not allowed → blocked
• Shows incorrect authentication error

? This makes troubleshooting confusing.

? Why Thunderbird Worked

⚠️ Common Mistakes

• Using normal Gmail password ❌
• Ignoring outbound routing rules ❌
• Assuming SMTP settings are wrong ❌
• Not checking Google Admin policies ❌

✅ Best Practices

• Always check Routing Rules in Google Admin
• Use App Password for Outlook IMAP/POP
• Prefer OAuth login where possible
• Avoid strict outbound restrictions unless necessary
• Test with multiple clients

? Conclusion

This issue is not a simple SMTP configuration error. It is caused by:

• Google Workspace routing restrictions
• Authentication method mismatch
• Outlook’s strict SMTP validation process

By allowing your domain in outbound routing and using an App Password, the issue can be resolved completely.