Selecting from which accout I want to send mail from

Question

On my 17" powerBook, when I go into mail and want to compose a new mail, in the header it gives me a drop down menu to select from which mail account I want to send the mail from.
Now on my desktop G5, that DropDown menu is no where to be seen. I cannot figure out where or how to turn that feature on. I have both computers logged in at the same time and have compared all the settings between them and they all match.
PLEASE
how do I get that dropdown menu to appear on my DeskTop G5
Thank you to anyone that can help

Answer 1

So, if I understand this correctly, you have ONE physical account, and you have one or multiple aliases that point to the actual user@realAddress of this one physical account.
In Mail>Preferences>Accounts>Account Information, it has:
Account type:
Description:
Email Address:
Full Name:
What do you have listed in the Email Address field? Is it
user@realAddress, aliasUserName1@aliasAddress1, aliasUserName2@aliasAddress2, ...???
If so, I would have thought that that should normally enable the Accounts field that I talked about in my previous post.
If that doesn't do it, why not create a second (temporary bogus) mail account? For example, you could create a temporary fictitious account using localhost as your smtp and imap/pop servers). It'll give you warning messages during setup because there is no server at localhost but that's okay, just continue onward to account completion.
Or create a real mail account at AIM (AOL) -- they're free and you can give that one out when you're worried about disclosing your email address. Go to http://mail.aim.com and create one, then go to http://help.channels.aol.com/kjump.adp?articleId=219584, which has the directions to configure Mail.app account preferences.
Then try the Customize header... thingy again. Then delete the fictitious account in Mail>Preferences>Accounts (or the free AIM account if you never intend to use it). Because once the multiple email addresses have been specified as your email addresses in the real original account, I would think that the Accounts field should stick. If not, I'm stumped for ideas.
I noticed you marked this post as "answered." But not solved? If anything in this thread was helpful to you, and if you are still able to do so now that it has been marked "answered," please consider awarding points to anyone here that posted worthwhile assistance. I'm kind of speaking for all of us and maybe I shouldn't be, but we (okay, I) would be most appreciative. Of course, on the other hand, if none of these posts were of any use to you, then obviously they deserve no credit -- in which case, you probably shouldn't have marked this question as answered because there was no working solution given here for future readers experiencing similar problems to leverage on. And if you solved it on your own, irrespective of what we all posted, everyone that is experiencing a similar problem like this, that reads this "answered" thread, would undoubtedly like to hear how you eventually solved this issue. And I would, too, just to learn something new.
Thanks, and I do hope that either something in this thread or your own self-discovery enables this functionality, one that Mail.app should be providing.
(if this solves your problem, or is actually helpful towards arriving at a solution to your problem, please consider marking this reply as "helpful" or "solved" in order to award points. This would be in addition to (if applicable) marking this question as "answered")