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+## Prerequisite
+
+You should not install PAHEKO on your main YunoHost domain, especially for sending mails.
+* Add a new domain for PAHEKO in YunoHost.
+  * If your main YunoHost domain was provided by YunoHost, e.g. `domain.nohost.me`, then you don't have to buy/register a new domain name.
+  * Just click on `I already have a domain`.
+  * Type e.g. `paheko.domain.nohost.me` and click on `Add`.
+* Add a Let's Encrypt certificate for this domain.