可是你给的link也说的不可以的。。。

whether the use is at work and on employer equipment. The employer should not look at private emails on a private email account that is password protected by the employee because the employee has a reasonable expectation of privacy, the account is the employee’s, and computer hacking laws provide protection against viewing personal emails without consent.

后面是对employee的忠告：However, employees should be careful about using those accounts and passwords on employer owned equipment, because that information can be stored in backups, is visible to monitoring software and may not really be private at all.