Sometimes when you change location you may find that your emails no-longer send from your email client (such as Outlook, Thunderbird, MacMail, Windows Mail, etc) this can also be the case if you change your ISP, for example from BT to Sky. You may see this as the error 0x800CCC0E
in your email program.
This is because to try and prevent spam, these ISPs block the port normally used to send email (25) which is useful to help with spam, but bad for people who don't know why this is happening.
To get around this problem you need to go into your email client's account settings and change the SMTP/Outgoing mail server port from 25 to 587 (often hidden in the 'Advanced' section). This shouldn't need to be changed in future so you don't have to worry about remembering to change it back again later. The reason this works is that most ISPs don't block the other standard email port which allows you to get around the block they have in place.
Still Unable to Send...
If you are using your ISP's SMTP/Outgoing server and you don't have "My Outgoing Server Required Authentication" enabled then you may run into another problem. This problem is that ISPs that don't use authentication only allow you to send email from the Internet connection that you have with them (i.e. your home broadband connection).
To tell if you're using your ISP's outgoing mail server go into your email client's "Account Settings" section and look at the server address. If it contains the name of your ISP in it then chances are you are using their SMTP (outgoing mail) server. In this instance you will need to contact your ISP and ask them if they have any way of you sending email whilst away from home.