If you want to open registration for any domain, you have to setup the allowed domains with ma1sd's `blacklist` and `whitelist`. The default behavior when neither the `blacklist`, nor the `whitelist` match, is to allow registration. Beware: you can't block toplevel domains (aka `.xy`) because the internal architecture of ma1sd doesn't allow that.
```yaml
matrix_ma1sd_configuration_extension_yaml: |
register:
policy:
allowed: true
threepid:
email:
domain:
blacklist: ~
whitelist: ~
```
## Troubleshooting
If email address validation emails sent by ma1sd are not reaching you, you should look into [Adjusting email-sending settings](configuring-playbook-email.md).