Is This A DNS Issue - Confused?

I have a domain www.domain.co.uk live on my webserver at the moment. Its nameservers point to this server.

I also have a 2nd webserver that I am preparing to take live. Once testing is complete I plan to shutdown the first server and point the nameservers to the ips of the 2nd one.

So I have setup the domain www.domain.co.uk in the DNS on the 2nd server and given it an A record with this servers ip. This site is just a static HTML page with a Contact Form which sends me an email. But despite having setup SMTP the (2nd) webserver is not sending emails - they just sit in the Queue.

My ISP tells me that the problem lies because the 'website should point to the webserver ip' but I dont know what this means.

I have tried to research this subject online but cannot find any specific information about how an SMTP server decides whether it can SEND an email from a specific address. I understand that the MX record tells a a mail server where to send an email but is there a similar record which a mail server checks as regards the originating email?

Thanks

Chris

Doesn't sound like a DNS issue to me. The sending SMTP server needs to be able to correctly resolve the IP of the receiving SMTP server. It doesn't need to do anything with the sender address.

It sounds more like you have a problem on either of the mail servers or possibly with a firewall.

So you have both servers set up for the same domain, but at the domain registrar, the 1st server is where the nameservers point to? I'm guessing you are not actually able to send from the 2nd server because of this. You are attempting to send mail from domain.co.uk which references a different IP's nameservers. You can set up your 2nd server to send mail locally, but until the nameservers are referenced correctly, you wont be able to send mail.