You can send mail from a domain alias by creating a ‘custom from:’ address in your individual email account. This is a personal account setting and not a domain-wide setting. You can’t currently enable a ‘custom from:’ address from your control panel.

To display another email address in the ‘From:’ field, follow these instructions in your email account:

1.Click Settings at top of any page in your email account, and then select the Accounts and Import tab.
2.Click Add another email address in the Send mail as: section.
3.Enter your full name in the Name: field, and the email address you’d like to send messages from in the Email address: field.

4. Click Next Step >>, and then click Send Verification to continue the process.

Google will send you a verification message to your email account to confirm that you’d like to add the address as an option in the ‘From;’ field. Click the link in that message, or enter the confirmation code in the ‘Accounts and Import’ section of your email account, to complete the process. Once you’ve verified that you’d like to add the address to your account, you can start sending messages using your ‘custom from:’ address.

Note: Your primary address will still be included in the full headers to help prevent your mail from being marked as spam. Most email clients do not display the sender field, though some versions of Microsoft Outlook may display ‘From custom address on behalf of username@mydomain.com .’