You need to design a strategy for providing e-mail access to the subsidiary users. What should you do？（）
- ADeploy POP3 and IMAP4 services on Exchange front-end servers. Make the front-end servers accessible from the Internet by means of POP3， IMAP4， and SMTP only
- BDeploy Microsoft Outlook Web Access on Exchange mailbox servers. Make the mailbox servers accessible from the Internet by means of HTTPS and SMTP only
- CDeploy Microsoft Outlook Web Access on Exchange front-end servers. Make the front-end servers accessible from the Internet by means of HTTPS only
- DDeploy an additional Exchange mailbox server that contains all subsidiary mailboxes. Deploy Microsoft Outlook Web Access on the server. Make the server accessible from the Internet by means of HTTPS only