office 365 , outlook 2016, MRM ,

Hi experts

what will happen when MRM applied user mailbox , https://technet.microsoft.com/en-us/library/dd297955(v=exchg.160).aspx#MRM

what ever it does to user mailbox , it really deleted user email back to 2015 so all mails prior to 2015 like 2014, 2013, 2012 were gone.
i look in everywhere like there mailbox and in place-archive , only show 2016, 2015. only effected on default native like inbox , sent folder , junk etc... but not personal folder (sub-folder ) got created by user, all mails were there , so no problem on those subfolder (personal).

but sent item all gone 2014 , 2013 etc.. some inbox were missing to but since inbox they moved to sub-folder but sent item were very MIA.

I tough MRM only effect when user choose to use policy RTP , or is ti applied automatic to those folders like sent /inbox/junk ?

Thank you in advance alls