According to their response to this idea in the Idea Exchange:
Status: Not Likely
We have strategically chosen POP3 Email architecture to minimize storage costs. Please know that each master email account has 2GB of storage and if the user does not POP their email, the email is accessible from anywhere with internet access via myverizon.com.
You are welcome to vote for the idea, but Verizon doesn't seem to be interested in IMAP.