.... Unless they have reasons to. sometimes, just as a measure against industrial espionage, some companies do practice random screening of emails... and maybe even phone calls. u can verify this with risk analyst... actually its quite a standard guideline under certain school of corporate risk assessment, analysis and countermeasures.

but there are some cases where paranoia is the driving force.... well we are dealing with humans after all.

U already did that... dint u read your employment contract/offer letter? furthermore its a standard clause in the company handbook. they dont need to inform or remind the staff anymore cos it was already given to u to acknowledge and signed before u were hired.

furthermore... there's no privacy in the office as long as its office property. they can walk in and use masterkey to open ur drawer and check its content, etc. the only privacy is they cannot do a body search nor go thru your purse/handbag/wallet etc.