Why is all my email downloading again after reinstalling Outlook?

In this excerpt from
Answercast #59, I look at several configurations that would result in email
being kept on the server and ultimately downloaded again with a new instance of
Outlook.

Replicating emails

So, it’s not a real clear problem, but I have a couple of suggestions or
things to look at least.

In part, it really depends on how Outlook was originally configured.
Normally, what happens is that the most common configuration uses POP 3 to
download your emails. In downloading your emails, it actually removes them from
the email server. In other words, it actually moves the email from
your email service provider’s computer server to your computer into your
Outlook PST file.

Now, in a case like this, there are two scenarios that could result in the
emails being downloaded twice.

Leave messages on server

One is that there’s an obscure setting in Microsoft Outlook. You have to go
in Account configuration, into the Advanced
settings, and there’s a checkbox called Leave messages on
server.

What that does is that still uses POP 3 to download your messages, but
instead of deleting the server’s copy of the messages after they’ve been
downloaded, they stay there. Those copies are still there. Microsoft Outlook
simply keeps track of how much it’s already downloaded.

The problem arises when you configure up a new instance of Microsoft
Outlook. It doesn’t know which emails have already been downloaded and as a
result, downloads them all again. That could be what you’re seeing.

Now, the reason I say it “could be” is that it’s not common. It’s very
unusual for this Leave messages on server to be checked. It’s not by default,
it’s done specifically by the person who’s using the computer. So I would
expect that that’s something you would have realized; you would have known
about it and you would have remembered setting it.

IMAP protocol

The other approach is if you’re not using POP 3, but you’re using something
called IMAP.

IMAP is a different kind of protocol for accessing the emails stored on your
email server. Instead of moving your email from the server to your PC, it
actually mirrors the email from the server on your PC.

What that means is that the master central repository for your email is
considered to be your email server. Your instance of Outlook on your PC is
really just a window on that.

• If you read an email, it’s marked “read” on your PC and on the server.

• If you delete an email, it’s deleted on your PC and on your server.

• If you move an email to a folder, that folder is created, and the email is
  moved on both your PC and the server.

So that way, if you are creating a new instance of Outlook and configuring
it to connect to this server using the IMAP protocol by definition, it’s
going to give you a new window on all of your email. Yes, that typically does
mean it’s going to download all of your email once again since this is a new
instance of Outlook, a new copy of your email.

IMAP and Gmail

Now the one place where it can get confusing is if IMAP is used with Google
Mail.

With Gmail, by default, when IMAP is used with Gmail, the delete operation
actually doesn’t delete.

Remember that Google Mail, Gmail, is based around an archive feature. In
general, you don’t delete your email – which keeps it in your email
folder. It keeps it in your email system; it just keeps it from being
viewed in your inbox any more.

Now when IMAP enters the picture, IMAP is going to say, “When you delete
something on your PC, tell the server, ‘Hey, delete this.'”

If you configure Gmail with its default settings, it’s actually not going to
delete; it’s going to archive (there’s a default setting that you might
change).

Check your settings

So those are the kinds of things that can lead to what you’ve described.

I can’t say which one it is specifically in your case. But I would:

• Look at the “Leave messages on server” option, if you’re using POP 3;

• Or, understand how IMAP is working for you if in fact you’re configured to
  use IMAP for your Outlook email access.