title: How to send e-mail from non-existing (autogenerated unique id) email?
body: <p>I'm the owner of a domain, and I'm currently hosting its mail (MX) in Google Apps for Business.</p>
  
  <p>I have a catch-all account, so if someone replies an e-mail to <strong>generated-unique-id@mydomain.com</strong>, I have a robot that will read that e-mail and do some processing.</p>
  
  <p>Problem is: How can I send an e-mail from that sender's address? I mean: I cannot create a userid for every generated id, and if I authenticate into Google SMTP with some user, the sender is automatically filled as that user address. (I'm aware that I can use any "verified aliases" as sender (or reply to), but I also cannot create an alias for every generated id.)</p>
  
  <p>In summary: <strong>I need to send emails from non-existing e-mail address.</strong> How can I do that using 3rd party existing services (I don't want to host my own SMTP server, unless there is no easier solution).</p>
  
  <p>Are there any hosted mail servers that will allow me to do that?</p>
  
  <p>PS: As you may guess, <strong>it's a ticket-like system that should generate an unique e-mail address for each thread</strong>. (Yes, I know that I could use Subject for the unique identifier. Is that the best solution?)</p>