If you are going to have a lot of heavy traffic on your website then using a hosting service is a very good idea, especially if you have a lot of graphic or dynamic content. Webservers and mail servers know nothing about each other. All you need to do if you haven't already done so is create and 'A" record for you mail server. To do this just point the name of you mail server, let's say mail.yourdomain.com to the ip address of your mail server. Then edit your 'MX' record to show that mail.yourdomain.com will handle the mail for yourdomain.com. If you have a huge amount of mail coming into your server, you may want to add a secondary mail server in case your primary goes down. If mail is very light, then this is not necessary because most mail will be queued on the sender's server for a few days or so.