A number of ISP's block outside port 25 connections on their customers accounts. This is a technique to help prevent spamming. If you are using an ISP that has port 25 filtering implemented, to send and receive your email from Simplehost you will have to make a small change.
Port 25 is used for outgoing mail connections (also known as SMTP). When attempting to send email to Simplehost you may see an error in your email client similar to "could not connect to the outgoing mail server (SMTP)"
Most ISP's allow the use of the submission port (port 587) which is a way to still use the simplehost mail server. To do this in your email client instead of using port 25, try changing to port 587.
To use your ISP's mailserver for outgoing mail
Change your outgoing (SMTP) server in your Email Accounts settings to your ISP's mailserver - this is usually provided on sign-up or can be found on their website in frequently asked questions.
Example - for Telecom: send.xtra.co.nz
Here is the full list of Telecoms settings: http://telecom.custhelp.com/app/answers/detail/a_id/1594/p/193,0
No other changes are required and you will be sending your email out through your ISP's mailserver -- your email will still appear from your Simplehost email address and you will still receive email on that address from Simplehost.
Some ISP's offer a choice to opt-out of port 25 filtering, see your ISP's information to find out how.