According to a German security researcher site, When you enter your POP / IMAP e-mail credentials into a Blackberry 10 phone they will be sent to Blackberry without your consent or knowledge. Apparently a server with the IP 188.8.131.52 which is in the Research In Motion (RIM) netblock in Canada will instantly connect to your mailserver and log in with your credentials.
If you do not have forced SSL/TLS configured on your mail server, your credentials will be sent in the clear by Blackberrys server for the connection. In otherwords Blackberry thus has not only your e-mail credentials stored in its database, it makes them available to anyone sniffing in between. This basically gives a way for NSA and GCHQ to use Prism to spy on you.
The site suggests deleting your e-mail accounts from any Blackberry 10 device immediately, change the e-mail password and resort to use an alternative mail program like K9Mail.