Troubleshoot network traffic issues

G Suite Sync for Microsoft Outlook

If you're having network-connectivity issues with G Suite Sync for Microsoft Outlook (GSSMO), here are some steps that can help you fix the problem.

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Fix connectivity issues

Step 1: Open network ports
  • Open port 443 for Outlook.exe and ProfileEditor.exe. Our synchronization products communicate mostly on network port 443 so this action can resolve many issues. For details, consult your Microsoft documentation.
  • Reinstall GSSMO from its download page to ensure the installation files download correctly.
  • Open port 80 to download the Certificate Revocation Lists (CRL).
  • Open ports 80 and 443 on Microsoft Windows firewall to allow Outlook to communicate with Google's servers. For details, consult your Microsoft documentation.
Step 2: Allow traffic from permitted URLs

Approve the following URLs:

URL Purpose
Authentication Calendar
Certificate Revocation Lists Contacts Global Address Book
Mail Notes Tasks


Note: If you're using a Windows parental control system, you might need to add URLs to your allowlist. For details, consult your Microsoft documentation.

Review how to find Google IP address ranges. GSSMO can use any one of these IP addresses.

Step 3: Check if you're using a proxy

GSSMO doesn't support authenticated proxies. To detect if you have a proxy:

  1. Close all Microsoft Internet Explorer windows.
  2. Open a new Internet Explorer window.
  3. Go to
  4. If you're prompted for proxy authentication, contact your network administrator for help.

Google Cloud Support doesn't offer assistance with connection issues when a proxy is in place.

Step 4: Consult the log files

Network problems are logged in GSSMO's trace files. Use the Log Analyzer to analyze your trace logs. Learn more

Troubleshoot common issues

Check the logs

If you have network errors (for example, a network timeout, connection refused, etc.) or SSL/TLS issues (for example, a secure connection problem), the logs show the IP address the tool tried to connect to. If there's a secure connection issue, the logs show the reason (for example, certificate name mismatch, certificate expired, CRL check was unsuccessful, etc.) and the certificate details (for example, a Google certificate or a HTTPS-inspecting proxy). This should significantly reduce the need to get network captures for troubleshooting, and applies to both the main logs (Trace-*.log) and the authorization logs (in the "Identity" folder).

Authorization log example

[] TLS connection failure. See details below. [Status: 0x00010000. Status Info: 0x00000001]
[] Certificate details:
Valid from: 2017-09-13 17:23:55 UTC
Valid until: 2017-12-06 17:10:00 UTC
Mountain View
Google Inc
Google Inc
Google Internet Authority G2
[] WINHTTP_CALLBACK_STATUS_FLAG_CERT_REV_FAILED: Certification revocation checking has been enabled, but the revocation check failed to verify whether a certificate has been revoked. The server used to check for revocation might be unreachable.
[] Error from API WinHttpSendRequest with WinHTTP proxy. Will try direct (without proxy). Code: 0x00002f8f
[] Network connection destination details: (

In this case, the year in the machine's current date was changed to 2022, making the certificate seem out of date. You can view the current date at the start of each log line, and the "Valid from" and "Valid until" dates of the certificate don't match the current date. The error flag WINHTTP_CALLBACK_STATUS_FLAG_CERT_REV_FAILED indicates the certificate revocation check was unsuccessful.

You can also view the destination IP address and the resolved hostname after "Network connection destination details" on the last log line. It's a address, meaning it's Google.

Trace log example

Note: This log example is from GSMMO. Similar trace log entries will also appear in GSMME, GSPS, or GSSMO when these products experience network/TLS issues.

2017-09-21T04:10:04.356-03:00 1a20 E:Network ClientMigration!WinHttp::HandleCallback @ 2025 ()> Secure connection failure. Status: 0x00010000. Info 0x00000009
2017-09-21T04:10:04.356-03:00 1a20 E:Network ClientMigration!WinHttp::HandleCallback @ 2030 ()> Failure details:
WINHTTP_CALLBACK_STATUS_FLAG_CERT_REV_FAILED: Certification revocation checking has been enabled, but the revocation check failed to verify whether a certificate has been revoked. The server used to check for revocation might be unreachable.
WINHTTP_CALLBACK_STATUS_FLAG_INVALID_CA: The function is unfamiliar with the Certificate Authority that generated the server's certificate.
Certificate details:
Valid from: 2016-09-20T04:08:45.000Z
Valid until: 2022-09-20T04:08:45.000Z
Created by
Created by
2017-09-21T04:10:04.356-03:00 1a20 E:Network ClientMigration!WinHttp::HandleCallback @ 2071 ()> Error result 5, hr = 0x80072f8f. Setting event 0000000000001638.
2017-09-21T04:10:04.356-03:00 1a20 E:Network ClientMigration!WinHttp::HandleCallback @ 2076 ()> Network connection destination details: (COMPUTERNAME)

In this case, Fiddler was installed and set to do HTTPS decryption (meaning it uses its own certificate), but its certificate was removed from the Windows trusted certificate list, so it's untrusted. Note that because Fiddler is a proxy, it was connecting to and not to Google. The error flags include WINHTTP_CALLBACK_STATUS_FLAG_INVALID_CA, which means the system doesn't trust the Certificate Authority (CA). Also notice Google did not issue this certificate.

The example text displayed here is easy to forge if you're an attacker, so it shouldn't ever be used for authentication (use a CA signature instead). However, it's useful for identifying setup issues with firewalls/proxies that do SSL inspection/man-in-the-middle (MITM) attacks.

Note: Older versions of GSSMO might not include the advanced logging features discussed here. We recommend you update to the latest version. For details, go to Step 1.


Important: Our support team is happy to provide these guidelines for setting up your network to work with GSSMO. However, we can't assist with your network configuration. For help, contact your local network administrator.

Google, G Suite, and related marks and logos are trademarks of Google LLC. All other company and product names are trademarks of the companies with which they are associated.

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