how to create an "Alias" for an email address

Do you want the email address to show up as notifications@domain.com or do you want the friendly display name to show up as notifications?

To have the name that is displayed change you need to update the user object's Display Name value in active directory.
Open up Active Dirctory User and computers.
Exchange the Domain and Locate the users OU
find the user object "tech"
Double click the object.
On the general tab you will have a "Display Name" field. Whatever you put in here will be shown as the friendly name of the mail sender.

If you are trying to update the email address, then you will need to open up Active direcotry users and computers from the exchange server (on the program menu under Microsoft Exchange)
Find the "tech" user
Click on the Email addresses tab.
Create a new SMTP address with the value notification@domain.com and apply it.
Then select it in the list of email addresses assigned to the user and hit the "make primary" button.

i did change the display name but 2 minutes later this account sent a notification and it was shown as abc..should i update or wit a few mins?

This could be a lag in the offline address book update. are you running in cached mode?

how can i check if it runs on cache mode and change it ?