PushMail is where your email is pushed to a phone in the background and you get a notification when it arrives. To work around the lack of push notifications for Hotmail, Gmail and the like, PushMail takes a different approach.
Once you have set up PushMail, you will be asked to create an account, then forward email from Hotmail, Gmail, and whichever email services you use to the PushMail account. After PushMail gets the forward, it then sends a push notification to the iPhone. This will tell you Hotmail, Gmail or the like has email.
You do not have to have just the one email service going to the account, you could have Hotmail and Gmail (if you have both) going to your PushMail account. Without this feature your iPhone will have to check in your server to see if you have email, which means it will have to pull the email from your server.
Having this feature is great if you work for a big company and are not always able to check your email. PushMail costs around $4.99 so why not try it for yourself and let us know what you really think of this feature and how it worked out for you.
Source – theiphoneblog.com