Lruriawa it seems that you have specified a custom e-mail settings for the SMTP protocol, and instructed Flarum to send e-mail through this server (at Administration > Email). The SMTP server that FreeFlarum communicates with has sent a response with the error message above. It means that the SMTP server that you are using is “busy”, which usually means that it is overloaded and can’t process the request to send the e-mail at the moment, therefore the e-mail sending fails.
There is unfortunately no way FreeFlarum can solve this, as maintenance of the SMTP server that you have specified (ybrcadmin@...
) is not managed by FreeFlarum. I recommend that you contact the administrator of the SMTP server to resolve this issue. Meanwhile, you can of course send e-mail through FreeFlarum’s mail server through the noreply+...@freeflarum.com
e-mail address, which is usually sufficient enough for free forums that we host.