Add troubleshooting guide for unreachable mail addresses
@@ -54,3 +54,22 @@ Or, you can accept all content/MIME types: `--headers "accept=*/*"`.
See more info about the Accept header
[over at MDN](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept).
+
+
+## Unreachable Mail Address
+
+We use https://github.com/reacherhq/check-if-email-exists for email checking.
+You can test your mail address with curl:
+```
+ curl -X POST \
+ 'https://api.reacher.email/v0/check_email' \
+ -H 'content-type: application/json' \
+ -H 'authorization: test_api_token' \
+ -d '{"to_email": "box@domain.test"}'
+```
+Some settings on your mail server (such as SPF Policy, DNSBL) may prevent your email from being verified.
+If you have an error with checking a working email, you can disable this check using the
+[commandline parameter](https://github.com/lycheeverse/lychee#commandline-parameters) `--exclude-mail`.
+
+
+
