I would change to imap - that leaves the messages on the server, whereas pop pulls the messages off the server onto whatever device you are using, so if you are using more than 1 messages sent/received on deive 1 won't be visibe on device 2 and vice versa.
I would check your outgoing server details - do you get an error message or does it time lut when trying to send? It could be you have the wrong port number.