When sending messages from abroad you need to know the SMTP server for the ISP you are using. If you are in a hotel for example, they may tell you what that is for their Spanish ISP. The incoming POP3 server stays the same.
Option two is to use webmail to send replies but if your computer is not set to "Leave messages on the Server" whilst you`re temporarily abroad you won`t see them in webmail because they are now on your machine. (Hope that makes sense)