A.the best option is to change the imap4 retrieval settings on -ex15.
B.the best option is to access the -ex15 and disable the imap4 mailbox feature for the mailboxes.
C.the best option is to configure the windows firewall on -ex14 to block tcp port 25 and 110.
D.the best option is to configure the windows firewall on -ex14 to block tcp port 110 and 995.