iPhone: Rule based email forwarding? Is there a way to establish rules for mails processed on the iPhone (4s, iOS 6.1.3)?
In my case, I am interested in automatically forwarding certain emails to another email account once I receive them.
At first glance it isn't possible in a stock installation of iOS 6 and using the default mail app. If you jailbreak your phone, it appears that at least one tweak, Mail Enhancer Pro, will allow you to have rules on your iPhone itself.

However, there are a number of good options, other then jailbreaking, that may work.

First, if you use an IMAP email account, then you may be able to use your computer to route the mail. The changes will obviously reflect on the device. For example, if you have a Mac, then you can use Mail.app to create a rule to forward particular emails to the address you desire.

Second, depending on who provides your email, you may be able to route the mail there. I would say Gmail is an example of that. If you go to your Gmail account and navigate to settings, you can set up rules in there.

iCloud mail provides rules as well. If you go to www.iCloud.com -> Mail -> Settings (icon in the upper left corner). You can select the Rules tab and set up actions that would work apply to the mail you receive to your @me.com, @icloud.com, or @mac.com account.