For a shared mailbox i have given full access and send as permission to office 365 users. One of my user only uses shared mailbox to send emails. When user composes a new email the user every time from From Filed has to select shared mailbox. is there any option that i can make default From field as shared mailbox address rather than users email address.
Outlook works via outlook profiles, if you sign in to outlook via your profile then Outlook will default the from address to that.
If you would like to default the shared mailbox address as the from address then you will need to give the shared mailbox a password in AD and enable the account, then create a outlook profile for the shared mailbox separately and take yourself off as a delegate.
Once Outlook recognizes your shared mailbox as default, it will start to default your from address.
You can add both your user mailbox and shared mailbox profiles in Outlook and switch between the two.
@Vasil Michev If the shared mailbox is added to a profile as an account while is in the profile as shared, it will be buggy. You need to remove automatting or use a second profile just for the account.