[banden]

Yahoo is sketchy for IMAP/POP in general outside of paid accounts. From my experiences with my users, the following settings only work through the verizon network (not through WIFI.) Also it seems to just stop working randomly and you need to power cycle the phone to get it to reconnect.

***Incoming server settings***
Username: full email address
Password: Yahoo Password
IMAP Server: imap.mail.yahoo.com
Port: 143
Security: None

***Outgoing Server Settings***
SMTP Server: smtp.mobile.mail.yahoo.com
Port: 587
Security: None
Requires Sign-In: enabled
Username: Full email address
Password: Yahoo Password

Of note: Paid Yahoo accounts don't seem to have any issues.