Helping people with computers... one answer at a time.

A problem like this really depends on how Outlook was originally configured, whether you are using POP3 or IMAP, and how the email server is set.

My question is why does Microsoft Outlook replicate all of my past emails that I've already looked at, answered, and dealt with? So far, I have almost 7000 emails that are being copied to my inbox and having a time stopping this situation. The situation seems to have started after we replaced a modem or router furnished by our internet supplier and a call to them was answered by them to delete Microsoft Outlook and install them again. This would of course delete the last six months of work emails that I need to keep for at least one calendar year. I'm using Windows 7 and a powerful Dell laptop. Any ideas would be appreciated and by the way, I've been all over Google regarding this without a clear answer.

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.

Next from Answercast #59 - Why can't I send email via my MiFi?

Article C5895 - October 8, 2012 « »

Share this article with your friends:

Share this article on Facebook Tweet this article Email a link to this article
Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

PC Resolver
October 8, 2012 10:25 AM

I am one of those that tick the 'leave messages on the server' box - it's like having a backup of your messages.
My solution when re-installing Outlook is to immediately create a rule to forward new emails to a 'Temp' folder.
When it has finished I select all new emails and move them to the inbox. Then delete the folder.
I know it's a pain having them come down twice but at least it minimises the housekeeping.

Bruce Mandate
October 9, 2012 6:04 PM

I have pop mail and unchecked 'leave mail on the server' in Thunderbird' with the leave mail on the server for no more than 14 days. My mail has been staying on the server for 14 days. I've moved contacts to Thunderbird with 'yahoo_ab.ldif', but the other direction? My question then is, "Is it possible to push individual emails from Thunderbird back to the server?" I just read this link:, but since I'm only using one device, there's not the need for IMAPI. I would, however, like to have a backup for inadvertent deletions from Thunderbird post 14 days, or as a backup and, or access from another computer.

Mark J
October 10, 2012 1:43 AM

If you set Thunderbird, or any email program, to access your email through IMAP, any email in your emails program's folders will be automatically uploaded to your email server.
How do I backup my Yahoo! Mail? explains how to set up Thunderbird for Yahoo IMAP access.

Comments on this entry are closed.

If you have a question, start by using the search box up at the top of the page - there's a very good chance that your question has already been answered on Ask Leo!.

If you don't find your answer, head out to to ask your question.