What does Treat as an alias do in Gmail?

Question

When you set up a new account on Gmail to be able to send messages from that account, one of the options to choose from is Treat as an alias. The only documentation I found about the feature is this page, but after reading it, I'm still confused as to what the feature does.

Questions:

• What exactly does this feature do?
• When would I need to use it?
• What other side effects does this feature have?
• Before this feature existed, were accounts treated the same as today's accounts with the "aliases" feature checked or not checked?

For the following examples, assume account A is my normal Gmail account, and account B is another Gmail account I'm using via account A.

How does the setting affect (or not affect) any of the following?

• Can I still use from:B in order to filter outgoing messages from B?
• When sending a message from account B via A, does any reference to account A exist in the email headers or full text?
• When I get an email sent to account B, and I press reply, the "from address" is automatically populated with account B. Is this feature changed in any way?

Answer 1

Gmail has a notion of "me" as a sender and recipient, which is why searching your mail "from:me" works.

If you choose "Treat as alias," Gmail will treat the other address as "me" in addition to your main Gmail address. If you untick "Treat as alias," then it won't. Before this feature was added, all "send mail as" addresses were treated as aliases, or in other words, treated as "me."

There are a few minor repercussions. For example, if you send a message to "me," Gmail will put the message into your inbox. So if you send a message to address B, then Gmail will put it in the inbox if B is treated as an alias, but will not put it in the inbox if B is not treated as an alias.

"Treat as alias" does not affect whether your other address shows in the headers; that feature is controlled by your choice to use an SMTP server for the other address. It will also not affect specific searches for the other address, or your default reply address (e.g. "Reply from the same address the message was sent to").

You should use "Treat as alias" if the other address represents your own personal identity. You should not use "Treat as alias" if the other address represents another person (such as your boss) or a mailing list.

When you choose to use the SMTP server for the other adress and do not check the 'Treat as alias' box, a bug in gmail occurs. All mail sent by you as account B will appear as sent 'to:me' in your Sent Mail box. See this thread. While this bug remains unfixed, it is highly recommended to use "Treat as alias".

Answer 2

By saying "treat as an alias" you're telling Google that it's your own address. The consequences of this choice are only realized in fairly specific situations:

• If you've told Google it is your own address, then if you put this address as a "To" (or Cc, Bcc) address, Gmail will simply place a copy directly into your inbox.
• If you've told Google it isn't your address (ie, it's not an alias), then if you put this address as a "To" (or Cc, Bcc) address, Gmail will still send the email as outgoing mail, treating it no differently to any other address.

Google may have made this a bit more intuitive if they'd presented it as a choice between the following two options:

1. This is my address
2. I am sending email on somebody else's behalf