Archive user mailbox when the user database near to limit

Hello Dear,

I have deployed a exchange server 2013 in my organization with dag solution.Also I have deployed another exchange server 2013 with only mailbox role for archiving user mail box.Now want to create a rule or a retention policy which is like as :-

1.A user mailbox database size limit is 2 GB when mailbox size near to 1.5 GB mail will archive.

Please suggest me or show me the way how can I do this ?

Thanks and Regards

Samiul Haq