You can copy and paste the following code into the Email Reply Theme to make your emails look like they are sent from gmail.

1. Desk.com gmail style email reply template.html

{% assign emails = case.emails %}
{% assign threadlength = emails.size|minus:1 %}  
{% for email in emails reversed %}
 
{% if forloop.first %}
 
{{email.new_html}}
 
{% if email.agent %}
{% if email.agent.signature %}
<div style="margin-top:10px;"> {{email.agent.signature | newline_to_br}}</div>
{% else %}
<p>
  --<br />
  {{email.agent.name_public}}<br />
</p>
{% endif %}
{% endif %}
 
{% endif %}

 
{% endfor %}

2. Desk.com gmail style email reply template.txt

{% assign emails = case.emails %}{% for email in emails reversed %}{{email.new_text}}
{% if email.agent %}
--
{% if email.agent %}{% if email.agent.signature %}{{email.agent.signature | strip_html }}{%else%}{{email.agent.name_public}}{% endif %}
{% endif %}
{% if forloop.rindex0 != 0 %}
On {{email.send_at | date: "%b %d, %Y"}} at {{email.send_at | in_time_zone: site.timezone | date: "%I:%M%p %Z"}}, {% if email.agent %}{{email.agent.name_public}} {% else %}{% if customer.id == email.from_customer.id %}{{customer.first_name}} <{{ customer.email }}>{% else %}{{email.from_customer.first_name}} <{{ email.from_customer.email }}>{% endif %}{% endif %}  wrote:
{% endif %}{% endif %}{% endfor %}