Configuring Apple Mail with Gmail Aliases

I am trying to use AppleMail and trying to configure to using gmail alias.

My primary email address is sid@mydomain.com and I have configured this in Apple Mail and able to send / receive messages properly. This primary email has an alias on my google apps for business sid-sales@mydomain.com

Whenever someone sends an email to sid-sales@mydomain.com, I receive it on sid@mydomain.com and on the Apple Mail. So far good.

Now, I want to configure Apple Mail so that I am able to send emails using both my primary email and the alias (and with different names). So, I want to have two email configurations -

- Sid <sid@mydomain.com>
- Sid from Sales <sid-sales@mydomain.com>

I am not able to get this working. I tried adding both the emails separated by a comma in the Accounts section. After doing this, both the emails appear in the From field and I can choose from one but the receiving side is always getting my email from my primary email address. So, if I choose sid-sales@mydomain.com in the From field, the receiver still sees sid@mydomain.com

I also tried changing the plist file by adding EmailAliases - I was able to change the Name but the email address is still sid@mydomain.com

Can somebody please help me with this? I tried searching a lot on the internet but I am not able to find anything which will solve the problem.