I have a domain name which currently points to a shared hosting service. I've set up a dedicated Apache server for the web hosting, but would like to keep using the mail server of the old host.
Is the correct way to do this to add an A record that points to the IP of the new server, and an MX record that points to the hostname of the mail server? does anything need to be done with the NS records?
The Nameserver (NS) records do not need to be changed as long as you want that nameserver to continue as the SOA for your domain. What you stated would be correct, point your A record to the web server and your MX record to the mail server. You probably also want to make sure you have an SPF record setup as that is required by a large number of mail recipients anymore (slightly out of the scope of this question but still worth mentioning). I would also prep for the change by ensuring the TTLs on the current records are as low as your NS provider will let you set them to ensure the change takes effect as quick as possible.
