We have a client running SBS2008 and recently emailing was fine. We gave access to a web developer to add CNAME entries into our Netregistry DNS portal so that he could host the clients website.
Ever since they made changes - my clients can't receive emails but can send ok.
Anyone attempting to send them an email results back in an immediate bounce back stating 'error 550' no such user here.
This error occured last week and i found the web developer had put in his server for our clients MX records - Immediately i rectified this MX record back to mail.company.com.au and emails were fine. Then 2 days later the problems resurfaced again. I made sure DNS records remained intact but I am unsure what to check here. Netregistry support advise the MX records seem to be propagating correctly.
In my DNS manager I have:
MX record pointing to mail.company.com.au which is a FQDN
3 CNAME entries with one for autodiscover
Can anyone enlighten me as to what may be the issue here?