title: Add Send-As email (request) with domain name outside of current account
body: <p>Due to a merge, we have domain A under one Google Apps acccount, domain B under another one. I can create accounts for all the users in domain B to domain A to start a migration afterward. Adding aliasses with domains under account A is no problem. </p>
  
  <p>However, sending email as the account under domain B (which users can request manually with their account, the account in domain B will then be mailed with the question whether they want to allow it) doesn't seem possible with the <a href="https://developers.google.com/admin-sdk/email-settings/#manage_send-as_alias" rel="nofollow">Admin SDK</a>:</p>
  
  <blockquote>
    <p>Any email address which <em>exists as a user or an alias on the hosted domain</em>.</p>
  </blockquote>
  
  <p>Is there any way to start the process users would enter into when manually requesting to be allowed to send mail as that other user / email address?</p>
  
  <p>Migrating the domain to it first is out of the question as apparently, a domain has to be completely shut down before it is allowed to be added to another Google Apps account.</p>