At the moment, when we send a mail via K2 to one of our customers, the sending mail is something like M23W83@onk2.com.
That looks like a spam mail adress and we can only change the display name of the sending mail. For us it would be very, very important to use our own mail adress as sender like "no-reply@<companyname>.com".
We are working on the ability to have the vanity domain name from the email sending address, but it will remain @onk2.com as that is the mail server managed by K2 Cloud. This will be a more friendly name, however, and should be better for your customers.