5.5.0 Smtp 554 Spam Email Prob?

Email prob? - 5.5.0 smtp 554 spam

We changed our domain host customers on Friday, but they can not send emails, reciving okay.

The DNS entries look like this:

@ IN A 81.27.98.69
@ IN MX 0 client-server IP-MIS
@ IN TXT "v = spf1 ip4: 81.27.96.0/20-todos"
ftp IN CNAME @
www IN CNAME @
SMTP CNAME smtp690.inetc.net.
Smtp690.inetc.net CNAME POP3.
Last in a 81.27.98.69
Webmail IN A
* IN CNAME @
E-mail to one of my clients IP address

do this, my mother, because everything seems ok, but unfortunately not by e-mail. Also the strange thing is that they can send emails to addresses from Yahoo, but also other areas of the following errors:

# 5.5.0 smtp; 550 - "The e-mail from the host refused DOMAIN.co.uk>

Has anyone any idea what could be the cause?

Cheers