My mother-in-law has what I consider to be an odd setup for her Paradise email. Wherever she goes, she needs to change the SMTP settings on her laptop to match the ISP of whatever connection she's using (POP setting remain as Paradise). For example, she has to use smtp.xtra.co.nz at her house, smtp.xnet.co.nz at my house, and smtp.paradise.net.net at their holiday home. This is the only way she can send emails.
Personally, I reckon that your email servers should be independent of your internet connection. Does anyone kow of a legitimate reason for this oddity?