Sending email problems....systems doesn't work

Hi, I send emails out and I keep getting a problem saying that the email recipient is not accepted by the server an error occured. We have checked and our server is perfectly fine with other emails.

Please can you help.

Thanks,  

Hi, can you make a screenshot of the issue? Are you having issues with only certain recipients or with all your emails?
What version of eM Client are you currently using?

Thank you,
Paul.

not sure how to check my version, but it’s certain reciepients…i have 4 team members on em client. and when I send it out it tends to be at random the email issue. we all working independently but off email client. We not connected in any way. 

Hi again, to check your version number please go to Help > About.
Can you please make a screenshot of the issue?
What mail service are you using?

Thank you,
Paul.

Hi Paul the version is 6.0.20648.0…

What mail service are you using?
Can you try to update to this version if the issue persists? http://www.emclient.com/dist/v6.0.20715/setup.msi

Thank you,
Paul.