How many "b"s can you find in:
Q: 554 5.7.1 unknown recipitent I'm trying to send an email to M@Danielmadison.co.uk (there are no attachments being sent if that would affect anything) and i keep getting the following message:  Delivery to the following recipient failed permanently:
 M@danielmadison.co.uk

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain danielmadison.co.uk by mxcluster1.one.com. [91.198.169.8].
The error that the other server returned was:
554 5.7.1 : Recipient address rejected: Unknown recipient"
This is coming from the email address:  mailer-daemon@googlemail.com
I am also sending my emails to the domain via GMail.  I've been trying for several days now, and I have no clue what to do, if I'm honest.  Would really appreciate some help

A: The problem here is that the recipient mail server is blatantly lying. It's sent an SMTP error code 554 5.7.1 that means it is refusing to relay mail, but in the human readable text, it states "Unknown recipient". Both cannot be the cause of the failure. Someone has deliberately configured the mail server to confuse and mislead.
In the case of the mail server refusing to relay, the problem is that the recipient's mail server is misconfigured; it has an MX record for the domain pointed to it, so it should be accepting mail for that domain. Not doing so indicates that it is misconfigured.
Further, blatantly sending back wrong error messages is confusing and leads to the loss of legitimate mail in the best case.
Your recipient needs to get their email service fixed. Until it is fixed, you'll need to find another way to contact them.

user
There are seventeen "b"s.
assistant