title: What is the format of AWS SES messageIDs?
body: <p>AWS' Simple Email Service (SES) assigns incoming email a 'messageID'. This is distinct from the email's <code>Message-ID</code> header, <a href="https://docs.aws.amazon.com/ses/latest/DeveloperGuide/notification-contents.html#mail-object" rel="nofollow noreferrer">as described here</a> (though it makes it sound like it's for <em>sent</em> mail, it's available on received too).</p>
  
  <p>This identifier is 40 characters, lower-case, alphanumeric, and - so far in my sampling - appears to always end in <code>1</code> (but that might not be universally true of course - where my account is located, or which server was used may be a factor).</p>
  
  <p>Is the actual structure, how they're generated, documented - or otherwise guaranteed and known?</p>