OSX Mail Add Alias - Cannot send ?

Hello,

I am trying to configure my work Exchange account.
I have 1 email address and 1 alias.

However, no matter what I try, I cannot manage to "send as" my alias email address.

I followed the instructions in this thread:
https://discussions.apple.com/thread/3532782

and it half worked. I do see the alias when I create a new email. However, when I send an email from the alias, it goes through as the main email address: the recipient does NOT see the alias.

anyone knows or has ideas on what to try?
I'm also trying to set that up on my iPhone and have similar issues (there I cannot even select the alias).

I have the latest software updates:
Max OSX 10.10.5
iOS 9.0

thank you

 

am I the only one using aliases?