If using a custom branding logo, that logo is placed into the email reports, too (between the Salutation and the first website). Two suggestions for improvement:
The logo is not restricted in size and gets really large if a large logo file is uploaded (which is actively suggested by the concerning admin page). See <a href='/5051'>#5051</a> for the decision that was made in the backend (less relevant) Position the Piwik or custom logo above the Salutation to the top left (seems to be default in email newsletters etc. and doesn't suggest that the logo belongs to the first website in the list but to the complete email).
This was initially reported in: https://github.com/piwik/piwik/issues/309
Not really needed I reckon?