Autodelete SQL Message Archives

Hey folks - I'm not a sql guru and am having problems running queries to setup my message archive to auto delete after 90 days.

The last function I found on these forums is this (for one month) but I'm getting errors. ("Now" is not a recognized function)

select * FROM ofMessageArchive o where sentDate/1000 < unix_timestamp(now())-2629743

I'm running MS-SQL external database. 

Thanks in advance!

Openfire Noob here!