Your company's network administrator has noted several instances of unusual activity suggesting that an attacker may be intercepting and potentially altering the communications between the company's mail server and remote clients accessing email over the internet. Which of the following strategies would be most effective in safeguarding against this type of network security threat?
Implement SSL/TLS for email transmission.
Deploy additional firewalls between the mail server and the internet.
Increase the frequency of password changes for email accounts.
Advise clients to only connect to the email server using a VPN.