emails/app/views/spree/shared/_base_mailer_header.html.erb
<!-- You can override this template to design your own header. -->
<tr>
<td class="email-masthead">
<%= link_to current_store.url, class: 'template-label' do %>
<% if logo_path.present? %>
<%= image_tag logo_path, class: 'logo', alt: current_store.name, title: current_store.name %>
<% else %>
<%= current_store.name %>
<% end %>
<% end %>
</td>
</tr>