Whatever branding you are doing, wherever it is, must be consistent in image and tone with the branding throughout your entire campaign.
Again, e-branding that differs from, or contradicts, the branding produced by the traditional advertising agency is problematic. A dropped connection between the two may confuse your targeting market.
Companies that have embraced email marketing have taken traditional methodologies and applied them to the email marketing world. The same tried-and-true methods work, if they're applied properly, in the email marketing world.
Conclusion Your e-branding must be consistent in image and tone with the branding throughout your entire campaign.