iPost uses a special type of encrypted token to keep track of the identity of each of your contacts when they interact with your mailings. As a convenient shorthand, this encrypted token is referred to as a blob, because it encodes several pieces of information lumped together. This 'blob' can be optionally appended to tracked URLs using email tracking parameters.
Note regarding GlobalEmailStatus and GlobalMobileStatus parameters
These parameters are assumed true if absent but corresponding Email or Mobile fields are present; they are ignored if present but corresponding Email or Mobile fields are absent.