[exim] What's the best way to secure both SMTP and POP authe…

I am currently using AUTH PLAIN via SASL for SMTP and then TLS. I have
nothing currently in place to POP3 but I am just wondering, I mean, if
someone was doing any packet sniffing they could see the username and
password being passed because of the fact that I am using plain. What is
the best and most secure way of preventing this for both SMTP and POP3
authentication?

Thanks,

Jon