If you have ordered a server from https://keriointhecloud.com/ then that server has a name. For example "kalibres.saas.tuxis.net".
In order to receive mail, you need to change the MX records for the domain name for which Kerio Connect should handle mail.
To do this add the following MX records (kalibres.saas.tuxis.net as example):
prio: 10 value: kalibres.saas.tuxis.net
If you want your own domain name to point to your Kerio Connect server, you can do so by creating a CNAME that points to, in this example, kalibres.saas.tuxis.net.
Suppose your domain name is cloudbouwer.nl and you want the webmail to be reachable at mail.cloudbouwer.nl.
Add in the DNS to cloudbouwer.nl a CNAME with the value kalibres.saas.tuxis.net
It is always wise to then set a valid certificate for mail.cloudbouwer.nl in your Kerio Connect server so that webmail users do not get a certificate notification.