How do I set MacMail to always send out from the same account?

Question

I have multiple email accounts for my business but have them set to forward to my iCloud address (because I also have an iPad and cannot get my business mail on that unless it's forwarded). When I reply to business messages I always want to use the business address and only occasionally want to use the iCloud address. Without changing the send out address EVERYTIME, which is what I'm doing now, is there a way to configure MacMail so that it will ALWAYS send out from my business address unless I specify otherwise?
I looked at Help and it says that you can set that preference in Composing, but it doesn't seem to work.

Answer 1

.mac/mobileme/iCloud is only one of many options you can use for Mail.   
In fact iCloud is shifting to mostly 10.7.2 or later only which your G5 does not support.
To determine if you can still use iCloud for Mail, read this tip.
POP account simply are either pop.mac.com, mail.mac.com, or mail.mobileme.com, or mail.me.com or pop.me.com.
smtp is the send mail server alone.   And issues with sending mail to a non-internet juice provider typically happen if your internet juice provider blocks any sendmail servers that aren't authenticated.   To solve that problem you need password authentication, and either a port 587, 2626, or 2662 with a username of your e-mail address, and password used for checking mail, and the sendmail server of your choice that knows of your e-mail address in your mail settings.
Using POP is great if you want to store your mail only on your machine.  Otherwise it is better to use IMAP which stores on the server, and lets you copy information up to your machine as you desire.