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小能豆

Sending mails with gmail from webserver

go

Long story short: I wrote a simple web server using Go and Sqlite to manage a little cloud service to storing documents. To access it, the user should receive a mail with the auth code. Since I’m still testing it, I decided to use my gmail account to send mails, testing it while sending mail to my other mail address (live.com) and itself. I set up an “app-password” on my google account and it worked perfectly fine, mails are arriving normally. After that, I decided to host it online, choosing Linode as provider. So I bought a domain (from Register.it) and routed it to the Linode instance. I run the web server and it works, but the moment I’m requesting a code, so when the server should send an email, it holds indefinitely and no mail ever arrive.

I’m still new to this kind of stuff so I’m looking for any advice who could help me understand what’s happening under the hood there.

Thank you so much!


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2023-12-18

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小能豆

When you encounter an issue where your Go web server, hosted on Linode, is unable to send emails while it worked locally, there are a few potential reasons to investigate. Here are some steps and considerations to help you troubleshoot the problem:

  1. Firewall and Network Configuration:
  2. Ensure that the Linode instance allows outbound traffic on the necessary ports for sending emails. If your mail server is using the SMTP protocol, it typically uses port 25. Some email providers may also use alternative ports like 587 (submission) or 465 (SMTPS).
  3. Check if Linode has any network-level firewalls or security groups that might be blocking outgoing email traffic.
  4. SMTP Server Configuration:
  5. Verify that the SMTP server details (hostname, port, security settings) in your Go code are correctly configured for the Gmail SMTP server. These details include the SMTP server address (e.g., smtp.gmail.com), port number, and whether SSL/TLS is required.
  6. Double-check that your Linode instance can resolve DNS and reach the SMTP server. Sometimes DNS resolution issues can cause delays or timeouts.
  7. SSL/TLS Certificates:
  8. If your mail server requires a secure connection (SSL/TLS), make sure that the Linode instance has the necessary certificates installed. Some email providers may reject connections without valid SSL/TLS certificates.
  9. Logs and Error Handling:
  10. Implement detailed logging in your Go code to capture any errors or debug information related to email sending. This will help you identify where the process is failing.
  11. Examine any error messages that your code generates when trying to send emails. Check for timeout errors, authentication issues, or other relevant information.
  12. Check for Rate Limiting or Restrictions:
  13. Some email providers, including Gmail, may enforce rate limiting or impose restrictions on sending emails. Check if there are any limitations on the number of emails you can send per day or per minute from your Linode IP address.
  14. Test with a Different SMTP Server:
  15. To isolate the issue, try configuring your Go code to use a different SMTP server (e.g., a local or public SMTP server) and see if it can successfully send emails. This will help determine if the problem is specific to the Gmail SMTP server or if it’s a broader issue.
  16. Linode Support:
  17. If you have tried the above steps and are still unable to send emails, consider reaching out to Linode support. They may be able to provide insights into any network or configuration issues specific to their platform.

Remember to handle errors gracefully in your code and log as much information as possible during the email sending process. This will assist you in diagnosing and resolving the issue.

2023-12-18