关于Certbot DNS-01挑战中带下划线的TXT记录无法被Google admin toolbox识别的原因咨询

Hey there! Let's break down why you're running into this confusing issue with your _acme-challenge.yourdomain.com TXT record not showing up in Google Admin Toolbox, while the version without the underscore works. Here are the most likely reasons and fixes:

• DNS propagation delay (the most common culprit)
  First off, rest assured that underscores are completely allowed in DNS TXT record labels (that's why Certbot uses them for the DNS-01 challenge!). The problem might just be that your new _acme-challenge record hasn't finished propagating across global DNS servers yet. Google's Admin Toolbox could be pulling from a cached version of your DNS data that doesn't include the new record, while the non-underscore version (if you added it recently too) might have had more time to sync, or was already cached elsewhere.

• Google Admin Toolbox input formatting quirk
  Sometimes the tool assumes you're entering a subdomain relative to the domain you're managing in Google Admin. For example, if your managed domain is yourdomain.com, entering the full _acme-challenge.yourdomain.com might make the tool accidentally query _acme-challenge.yourdomain.com.yourdomain.com (a double-domain mistake), which obviously doesn't exist. Try just entering _acme-challenge (without the full domain suffix) in the tool's input field instead—this often fixes the issue.

• Accidental misconfiguration in your DNS provider
  It's possible that when you added the _acme-challenge record, your DNS provider's interface had a hidden validation rule or you made a small typo that prevented the record from saving properly. Maybe you forgot to set the record type to TXT, or the value was entered incorrectly. Double-check your DNS provider's dashboard to confirm the _acme-challenge.yourdomain.com TXT record is actually present and correctly configured. The non-underscore version might have saved successfully because it didn't trigger any hidden checks.

Quick troubleshooting steps to verify: #

1. Use a command-line tool like dig or nslookup to check the record directly:

   dig _acme-challenge.yourdomain.com TXT
   

   If this returns your TXT value, the issue is definitely with Google Admin Toolbox's caching or formatting, not your DNS setup.
2. Wait for your DNS record's TTL (Time To Live) to expire—this can take anywhere from 5 minutes to a few hours, depending on what you set.
3. If you're using Google Domains as your DNS provider, double-check that you didn't accidentally create the record under the wrong domain or in a subdomain folder.

备注：内容来源于stack exchange，提问作者Amin Bou Hamdan