It maybe tempting to host your own email server but the following are 4 reasons why this is a bad idea!
Spam
When you are hosting your own email server you are responsible for weeding out the spammy emails. This is not an easy task when you are handling thousands of emails a day. If your daily email volume is less than 100 than this task can be doable but would you want to? Would you prefer someone like Gmail, Yahoo!, or Hotmail filtering out which email is spam and which is not? If all you receive is spam than it would be a nightmare trying to find a legitimate email from a group of spam emails.
Delivery issues
Is handling email delivery issues your full time job? Would you want to turn it into a full time job? If you run your own email server than you would be making it your full time job. There are many issues that can cause delivery issues. It can range from another email server rejecting your emails to your server not getting emails from someone else. When there are any email issues with Gmail, Yahoo!, Hotmail, Outlook, QQ, or any of the major email providers you will have to contact them individually and work with them to resolve the issue.
Antivirus issues
When downloading emails or looking at them. You may get attachments or other unknown surprises. Gmail and Yahoo! have their own security procedures to make sure the attachments that you receive or would download are safe. When you are running your own email server. You would be responsible for making sure all the attachments you receive is safe.
You are responsible for maintenance and updates
If you are running your own email server than you are responsible for checking for software updates and making sure they are applied correctly. This means checking in with the email server or subscribing to updates on the software that is being used on the email server. When you are using a third party provider they make sure this is done. When you are running your own email server you have to be on top of the software issues.