There is a domain name that has 6 email addresses tied to it and the DNS is just parked. If I change the domain name server, should I expect the email addresses to be affected?
Allow me to give you some information as to how DNS works and how e-mail works in relation to that.
Every domain on the web has "nameservers" attached to it. Usually there's a minimum of 2 nameservers. Nameservers, in English, are servers that are dedicated to providing DNS or address resolution to the domain in question.
So, if you have the domain "mydomain.com" with the nameservers of ns1.mydomain.com and ns2.mydomain.com - these 2 servers are both providing DNS records for this domain.
The reason we have more than 1 nameserver? Well, if the first fails, the second will take over and continue providing records.
How does it work?
NOTE: This is the easy explanation.
Someone types in www.yourdomain.com into their browser. Your ISP's DNS servers are checked to see if it knows about yourdomain.com already, and we can see that ns1.yourdomain.com and ns2.yourdomain.com are the nameservers for that domain.
We then ask ns1.yourdomain.com, nicely, what the IP address for yourdomain.com is. It responds with the address, our PC stores that information and then proceeds to try and load that site.
Why do we need DNS?
Without DNS the Internet would be an insanely boring place. To navigate websites you'd need to memorise the IP Addresses, and let's face it, most people can't do that. Why would I want to type in http://72.14.207.99 when I can just type in google.com? It's a matter of human preference, amongst other things.
DNS is essentially the translation of hostnames (google.com) to their relevant IP address counterparts (72.14.207.99), and vice versa. It works almost seamlessly behind the scenes so we don't have to worry about it.
So what about e-mail?
Typically, DNS usually functions on what's known as 'A' records for web traffic. 'A' records are basically yourdomain.com = 111.222.333.444 or some other address. E-mail, however, uses something called MX records.
MX stands for "Mail Exchange" and are a slightly different record type dedicated to... you guessed it... telling everyone where the e-mail for that domain goes to.
yourdomain.com - domain name this record belongs to
MX - type of record
10 - Priority of record
mail.yourdomain.com - Address to route e-mail to
The priority of these records is important, as this is essentially the list of servers it will try before it gives up trying to send e-mail for you. If the first server at priority 10 is dead and not responding, it will try the next priority (usually 20) and so on, until it either gives up or someone accepts the e-mail.
So, if you are moving nameservers, you need to ensure that the DNS records (in particular the MX records) are correct and up to date ,or your e-mail will potentially disappear into a black hole.
You can create a record on the new nameserver BEFORE the domain is hosted on it, without any problems. It's record just won't be used until you make the change. My advice is to copy the records across from new to old, and then update the nameservers accordingly.