Using a domain user account for SQL Agent works fine in SQL 2012 (and SQL 2005, 2008, 2008R2, 2014), you just have to give it the correct rights.
Act as part of the operating system
Adjust memory quotas for a process
Bypass traverse checking
Log on as a batch job
Log on as a service
Replace a process level token
It does not need to be a member of the windows Administrator group unless you enable the 'Automatically start SQL Server / SQL Agent if it fails'.
The Agent account will also need to be a Sysadmin account in SQL Server.
Original author: SQL Server FineBuild 1-click install and best practice configuration of SQL Server 2017 2016, 2014, 2012, 2008 R2, 2008 and 2005. 1 Dec 2016
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Disclaimer: All information provided is a personal opinion that may not match reality.
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