Emails not arriving "user unknown"

Emails not arriving "user unknown"

Hi
In my account I host two domains. My friend for which I run "bijaimee.nl" just informed me that here info@xxxxx can't be reached anymore. When trying to send an email to info@xxxxx , the sender receives an error: "550 5.1.1 <info@xxxxx > User unknown".

When I use my own Zoho (gabrie@yyyyy) account to send an email to info@xxxxx  it works and the email is received by her. The zoho account has two domains: yyyy and xxxx.

When externally sending an email to "user@xxxxx ", which is an alias in her account, that email is also received without issues. So it seems only the info alias has issues.

In my attempt to solve the issue I first switched the mailbox address from info to user, then removed info, then again added info and again set it to mailbox address. But it didn't seem to solve the issue.

Please assist in solving this.