How To Configure Your Custom Domain Email, Step 4: Thunderbird

Have you configured your CNAME records?

Have you configured blogger’s publishing settings?

Have you signed up for Google Apps?

Have you run an NSLookup?

Have you configured your MX Records automatically or manually?

Log into your email account and enable POP. (In Gmail, click on "Settings" in the upper-right of your email page, then click on the POP and Forwarding tab, then click on the Enable Pop radio button.)
Remember to SAVE your settings!
Next, open Thunderbird.
Select Tools.
Select Account Settings.
Click "Add Account."
Click the "Email Account" radio button, and click Next.
Enter your name in the "Your Name" field.
Enter your email address (e.g., namehere@customdomain.com) in the Email Address field. Click Next.
Select POP as your Incoming Server. Enter pop.gmail.com in the Incoming Server field.
If you want Thunderbird to store your email for this account in a separate folder, make sure the "Use Global Inbox" is NOT checked. Click Next.
Enter your full email address (e.g., namehere@customdomain.com) in the Incoming User Name box.
Enter a name for this account. Click Next.
Click Finish.
In the Account Settings panel, select "Server Settings" under whatever you named your account.
At the top of the panel, change the Port (which defaults to 110) to 995.
Next on the panel, choose the SSL radio button under Security Settings.
Under Server Settings, make sure the boxes are checked for "Check for new messages at startup" and "Automatically download new messages."
In the list of accounts in the Account Settings Panel, select "Outgoing Server (SMTP)" to reveal the Outgoing Server settings panel.
Locate the listing for your new account, highlight it, and click Edit.
You might want to change its description from "smtp.gmail.com" to something more easily identifiable (e.g., Custom Domain).
Make sure the server name is smtp.gmail.com
Change the Port to 587.
Under Security and Authentication, check the box for "Use name and password" and then enter your username (e.g., namehere@customdomain.com).
Select the TLS (if available) radio button.
Click OK.
Exit the Account Settings panel.
Click on "Get Mail" and enter your password when the box pops up and prompts you to do so. (Allow the password manager to remember your password so you don’t have to enter it each time Thunderbird checks the server for new emails.)