MobileMe: Using your mac.com and me.com email addresses
Summary
If you were a .Mac subscriber before the launch of MobileMe, you had a username@mac.com email address. Now that we have converted to MobileMe, you have also been granted a username@me.com address. These email addresses are aliases of one another, so they are one and the same and share the same inbox. You can choose to use either email address to send and receive mail on your computer, iPhone, or iPod touch and set up your MobileMe Contact and Calendar syncing.
Products Affected
.Mac Mail, MobileMe Mail, iPod touch, iPhone
Using me.com and/or mac.com addresses with Mail in Mac OS X 10.5
When you set up your MobileMe email in OS X 10.5 Mail, it will automatically list all of your MobileMe email addresses in the "From" drop-down box in messages you are composing. This allows you to choose to use your @mac.com address or your @me.com address anytime you compose a new message, inclusing any aliases you may have set up.
Note: Any aliases you created (and didn't delete) before the .Mac-to-MobileMe should have both @mac.com and @me.com versions. Aliases created after the transition can only be used with @me.com.
Set up MobileMe email in Mac OS X 10.5.
Using me.com and/or mac.com addresses with Mail in Mac OS X 10.4.11
Your MobileMe email address work the same in Mac OS X 10.4.11 as they do in 10.5. If you were an existing .Mac member and simply want to keep sending and receiving using your membername@mac.com address, you don't have to do anything. Note that all MobileMe features will appear as ".Mac" in Tiger, even if you are a new MobileMe member.
Note: Any aliases you created (and didn't delete) before the .Mac-to-MobileMe should have both @mac.com and @me.com versions. Aliases created after the transition can only be used with @me.com.
If you want to also use your new @me.com address, see the Mac OS X 10.4 section of this article.
Using me.com and/or mac.com addresses with a third-party email application
You can configure a third-party email application to use either your @mac.com or @me.com email address. However, depending on the email application you use, you may not be given the opportunity to choose to send from your other email address in the same way that Mail in Mac OS X allows. See this article.
Note: Any aliases you created (and didn't delete) before the .Mac-to-MobileMe should have both @mac.com and @me.com versions. Aliases created after the transition can only be used with @me.com.
Using your iPhone or iPod touch with a me.com or mac.com address
When using MobileMe Mail on your iPhone or iPod touch, it is recommended that you choose either your @mac.com address OR your @me.com address. Just choose the address you'd like to use and set it up on your iPhone or iPod touch. Note: Aliases are not currently supported on iPhone or iPod touch.