My emails out for new regsitered users have been working fine until .......

Yesterday a user registered with false details - eg. Mickey Mouse at email jddjdj@djdjdjdjdjdj.com.

I got the email telling me a new user registered which all looked normal and then about 20 mins later I got a delivery failure telling me the email couldn't be sent - Reason: Failed to connect to the recipients mail server. No DNS information was found for the 'jddjdj@djdjdjdjdjdjdj.com' domain.

Now the emails out on my site aren't working so if I register as a new user I do not receive the emails as a new user or the emails as the admin/host informing me a new user has registered.  Also trying to retrieve a password as a user who has forgotten my password no longer works.

The SMTP settings in Host settings still look correct but the Test doesn't work and simply reports: There is a problem with the configuration of your SMPT server.  The mail was not sent.

If I send an email from outlook using the same mail account the email gets sent fine.

Any ideas?  Could something on my site have been corrupted by this delivery failure or does something at the mail server need clearing/resetting.

The only way to know anything for sure is to check the SMTP logs.

Jeff