You might own multiple sites with multiple Gmail accounts using Google Apps! If so then I bet you are using a master email address to get all your emails at one place. GMail allows sync between your other email accounts. You can receive all emails from other GMail accounts in a single GMail account and reply those emails from the same email address where it hit first. You can also use GMail to check your email at other accounts that support POP3 access. The things is, GMail detects the frequency of incoming emails and decides to forward it according to the frequency level. Good thing is, you can increase the ability of GMail to check your other accounts for new email. Here it is how.