Depends where you work. If you work for a financial company, especially a brokerage, I think they are required by law to keep your emails on file for 7 years for regulatory reasons, and to have them ready and waiting to hand over to a SEC/OSFI/whatever auditor on demand.
However if you work for an unregulated company they may prefer NOT to keep the stuff around any longer than they have to. If a company has a policy of routiney deleting emails, then anything they routinely delete is not available for lawyers to "discover" via discovery motions, subpeonas, etc., and since it was deleted as part of a routine policy it's not an illegal act.
Of course the moment there's an ACTUAL lawsuit they have to stop doing that, because once they are aware of a lawsuit, deleting it would be destruction of evidence--but anything they deleted *routinely* PRIOR to the lawsuit is simply unavailable for the adversary to use againt them. (Going and shredding stuff because you realize you are about to be hit by a lawsuit is illegal--it has to be a routine policy predating any hint of legal action to survive in court.)
The company I work for now has an outright policy of not keeping emails around for this reason. They purposefully do not keep backups around longer than about a day, and they encourage employees to delete emails they no longer need. One I worked for previously had an outright policy of deleting ANY email that was older than a month out of your exchange folder, for the same reason--to ensure there was nothing available for anyone to discover should they ever face a lawsuit.