The way most people use gmail at work, it's possible for others to read it.
So far, in the jurisdictions which are most relevant to me, email and internet activity doesn't have the privacy protections which may be applicable to phone calls to/from a work telephone line/phone. So while it may be illegal for a company to tap the workplace phones used by employees and record all their calls without prior announcement, it may not be illegal for a company to tapthe workplace computers of employees and record all their activity without prior announcement.