Send & Receive Issues

How to Troubleshoot Gmail SMTP Connection Errors on Port 587 in UAT

Kushani Nimanthika Oct 9, 2026 868 views

Question details

Users need to resolve an issue where an application successfully sends emails via Gmail SMTP in Visual Studio but fails to connect in a UAT environment.

How to Troubleshoot Gmail SMTP Connection Errors in UAT

Product: Application Development / Gmail SMTP
Device & OS: not provided
Scenario: Deploying an application to a User Acceptance Testing (UAT) environment that requires sending emails through Gmail's SMTP server on port 587.
Observed behavior: The application connects to the SMTP server and sends emails without issues locally in Visual Studio, but the connection fails when running in the UAT environment.

Before you start

Verify that your UAT environment has an active internet connection and that you have access to your server's network configuration or firewall settings.

Solution 1Recommended

Consult Microsoft Q&A for Advanced Technical Support

This type of application and SMTP connectivity issue is highly specific to developer environments and is best resolved by Microsoft technical experts.

Because environment-specific SMTP failures often involve complex network routing, code configurations, or server-level blocking, standard software troubleshooting may not apply. Microsoft Q&A is the recommended platform to get direct assistance from application development experts.

Navigate to Microsoft Q&A

Open your web browser and visit the official Microsoft Q&A platform at https://learn.microsoft.com/en-us/answers/questions/.

Gather your diagnostic information

Collect your Visual Studio code snippets, application error logs, and details about the differences between your local and UAT environments.

Post your technical query

Create a new question detailing the Gmail SMTP port 587 failure, attaching your logs to receive specialized technical assistance.

Consult Microsoft Q&A for Advanced Technical Support

Provide complete details: When posting in Microsoft Q&A, ensure you redact any sensitive information such as actual email addresses or passwords from your code snippets.

Solution 2

Verify UAT Firewall and Port Restrictions

Before posting for help, perform a basic check to ensure port 587 is not being blocked by your UAT network.

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Frequently Asked Questions

Why does Gmail SMTP work in Visual Studio but not in UAT?

Visual Studio usually runs in a local development environment with fewer network restrictions. UAT environments generally employ strict firewall rules that block non-essential outbound connections, frequently including the SMTP port 587.

Do I need a special password for my application to use Gmail SMTP?

Yes. If your Google account has 2-Step Verification enabled, standard passwords will be rejected. You must generate an 'App Password' from your Google Account security settings and use it within your application's connection string.

What is the difference between port 465 and port 587 for Gmail?

Port 587 is the recommended port for standard SMTP mail submission with STARTTLS encryption. Port 465 is used for implicit SSL/TLS connections. If port 587 fails in your UAT, you might check if port 465 is permitted as an alternative.

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