Mail servers should theoretically be accessible from anywhere on the internet. This is because they have to accept mail (for their end users) from anywhere on the internet. Bottom line: you should be able to use the same mail server (POP3 and SMTP) wherever you are.
There is a caveat: some ISPs may block incoming POP3 connections (that's the "receive" part as far as you're concerned) from certain network addresses. You could check this point with your ISP.
Now, lets run some tests, from somewhere where you can't normally connect. Bring up a command prompt, and type the following:
telnet mail.skyscapes.com 110
This attempts to connect to your ISP's POP server, which runs on port 110. You should see a response similar to this:
Connecting to mail.skyscapes.com.
+OK <[email protected]>
To get out of that, press Ctrl+], then type "quit".
The test for SMTP is similar:
telnet mail.skyscapes.com 25
- the SMTP service usually runs on port 25, although I note from what you said above that they also accept SMTP connections on port 587.
Please report back your results from these two tests. When connected to a wireless network, are you usually able to browse the internet smoothly?
NB I connected fine to your ISP's server (POP3 and SMTP), so it doesn't look like they employ the blocking that I mentioned.