Clicking hyperlinks in Email messages becomes painfully slow

If somehow Internet Explorer is slow, then clicking links from Office will be slow as well, even if you don't use Internet Explorer as your default browser. So: check if Internet Explorer is still running fine.

Though you seem confident that DDE is to blame, Office has a surprisingly odd feature: it first uses an Internet Explorer component to see if the URL one clicks is valid. It does not identify itself as Internet Explorer; in the access logs one might see:

User Agent: Microsoft Office Existence Discovery

After that, it hands the resulting URL to the default browser. That is:

• If the hidden call to the URL yields some redirect, then the default browser is not even given the original URL, but the redirected URL.

• If the web site for some reason blocks the User Agent "Microsoft Office Existence Discovery", or if your Internet Explorer settings somehow prevents proper access to the site, then the link might seem dead while in fact using a normal browser it would work fine.

Ever wondered why your browser keeps redirecting you to some login page when clicking links from Office? Right: if Internet Explorer is not authenticated at the web site (especially true when it's not your default browser), then some sites might respond with a redirect to a login page, making Office forget about the URL you actually clicked...

Some more details about this funny annoying "Microsoft Office Protocol Discovery" at Microsoft's Description of the Microsoft Office Existence Discovery Protocol blog post:

When opening documents from a URL location in Microsoft Office 2007, the Office library can make an HTTP HEAD request to the web server for the opening URL. This request is sent with a User-Agent set to"Microsoft Office Existence Discovery". This call is new to Office 2007.

The purpose of the HEAD request is to check that the content exists at the URL location as a document, and not simply as a tempoary resource streamed down for a read-only session. The call will also attempt to obtain the last modified time of the content as returned by the web server in the HEAD response.

[...]

This call occurs on all URL open attempts, even if editing is not requested per se. As a result it is possible that the extra web call (made from the process space of the Office application in its network session and not the web browser in a separate session) can cause some users to see extra prompts to authenticate (401) or loss of session state and an unnecessary redirection (302) to a login page or other feedback form. This is expected behavior.

It seems this can be disabled using the registry; see my answer at MS Word validating links after click.

I'm getting a little bit closer.

Rebooting fixed the problem. :) Not that that is a permanent solution...

According to Microsoft programmer Raymond Chen, DDE is supposed to be obsolete, but everybody seems to still be using it.

The trouble with DDE, he says, is that it's cooperative, and one hung application can cause all other applications to not respond properly when they try to use DDE.

In my case, rebooting fixed the problem because it closed whichever application it was that was failing to respond properly to the DDE messages.

A common solution to this problem in the Windows XP timeframe was to uncheck the USE DDE box in the file type handler, but that checkbox appears to no longer exist in Windows 7. Even though DDE is obsolete, applications still register it in the registry so stupid apps like Outlook 2007 still use it to launch hyperlinks.

This solution wasn't very useful, because even stupider apps, like Firefox, were so intent on using DDE that they would REREGISTER themselves as using DDE every time they launched. The only permanent solution was changing the security settings on the appropriate key in the registry so that Firefox didn't have the ability to write to it.

I'm still not very happy with this answer.

I had a similar problem not too long ago, and the issue was definitely with Outlook, it became dead slow opening links and attachments. in my case it was the PST file which had grown beyond 4 GB.

Try compacting your PST or OST file:

1. Tools | Account settings
2. Click on the Data Files tab
3. Select your mailbox and click Settings
4. [Exchange mode] In the Advanced tab, click on the Offline Folder File Settings
5. Click Compact Now

MSKB has a few more tips: How to troubleshoot performance issues in Outlook 2007