i want to store outgoing mails To, From, and Bounce address and mailstatus. we can store them or not?
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I don't know. Can you?
Technology wise, it's simple. You can make backups of your mail spool. You can redirect copies of the mails. You can relay through a mail server that stores a copy. All depends on how you want to do it. And logs can store mail status and whatnot.
Legally, I'm not a lawyer, and it depends on what your HR department allows, what your government allows, what rights you're stepping on for your workers, and if they know about it, how tolerant they are of the creepiness of being spied on and how high your worker morale is. But it entirely depends on your situation. I'd also add that if you have a policy of storing emails this can change your status in certain legal situations; having it as a policy means you might be open to subpoenas for messages if you find yourself going to court.