I'm doing a site for someone who has their domain registered with 1and1 but I host all my sites with another company. I have set up the hosting and was going to change the nameservers of the domain to make it live but I'm not sure what issues this will create with their current email addresses. As long as the domain stays registered with 1and1, will the email addresses they have set up there still work?
Yes, it would still work. If you want to keep the mail server at 1and1 then what you need to do is the MX record and the 'A' Record for 'mail' points to the 1and1 server. If you want everything shifted to your new host then set up the email accounts at the new host and then the current DNS Records at 1and1, change the MX record to the new host. If you cannot do that then just keep the 1and1 account until the switch over is complete then for that day or two, check for mails at both ends.
Thanks eddy. So basically, if I just change the nameservers over but don't touch the email accounts that are already set up, they should continue to work ok?