Fixing the Post SMTP Slack Webhook Connection Error

If you're trying to set up Slack notifications with the Post SMTP plugin and encountering errors with the webhook URL (https://slack.postmansmtp.com), you're not alone. This is a common issue that many users have reported. This guide will explain the problem and provide the most effective solutions to get your Slack notifications working again.

Understanding the Problem

The Post SMTP plugin uses a third-party service at slack.postmansmtp.com to simplify the process of creating a Slack webhook. Based on user reports, this service can occasionally become unavailable. The symptoms of this problem include:

• A blank white screen when visiting the URL.
• A "403 Forbidden" error message.
• An "Index of /" server directory listing page.
• Browser warnings about an insecure or expired SSL certificate.
• An inability to authorize or generate a webhook URL.

These issues are typically caused by problems on the external service's server, such as expired security certificates, hosting changes, or server misconfigurations. These are outside the control of an individual WordPress site administrator.

Common Solutions and Workarounds

1. Wait and Retry

In many cases, as shown in the support threads, the team behind the Post SMTP service is aware of the issue and works to resolve it quickly. The problem is often fixed within a short period. If you encounter an error:

1. Wait a few hours.
2. Clear your browser's cache and cookies.
3. Try accessing https://slack.postmansmtp.com/ again.

2. Create a Slack Webhook Manually (Advanced Workaround)

If the automated service remains down and you need notifications immediately, you can create a webhook URL directly through Slack's platform. This is a reliable method that bypasses the third-party service entirely.

1. Go to https://api.slack.com/apps.
2. Click Create New App.
3. Choose From scratch, give your app a name (e.g., "Post SMTP Notifications"), and select the workspace it will belong to.
4. After creating the app, navigate to Incoming Webhooks in the left sidebar.
5. Activate the Incoming Webhooks toggle.
6. Click Add New Webhook to Workspace.
7. Select the channel where you want failure notifications to appear and click Allow.
8. You will be redirected back to the app page, and a new Webhook URL for Your Workspace will be generated. Copy this URL.
9. In your WordPress dashboard, go to Post SMTP → Settings → Notifications.
10. Paste the complete webhook URL you copied into the Slack Webhook field and save your settings.

Managing Multiple Webhooks

For administrators managing many sites, it can be difficult to identify which webhook in your Slack app settings corresponds to a decommissioned client site. To stop notifications for a specific site without deleting the webhook from Slack, a simple solution is to disable the notification within the plugin itself.

1. On the site you are decommissioning, go to Post SMTP → Settings → Notifications.
2. For the Slack option, select None from the dropdown menu.
3. Save the changes. This will prevent the plugin from attempting to send any failure alerts to Slack for that site.

Conclusion

Connection issues with slack.postmansmtp.com are usually temporary server-side problems that are resolved promptly. The most straightforward solution is to wait a short while and try again. For those who need an immediate and permanent solution, creating a webhook manually through Slack's API is a reliable alternative. For managing multiple sites, remember to disable notifications directly in the plugin's settings for a clean decommissioning process.