Microsoft says that Outlook freezes “by design” and that they are not going to be working on this issue. Below is their explaination and proposed solutions:

Issue Statement:

Outlook contacting server for information when replying/forwarding and printing emails with HTML contents and images.
The behavior that we are experiencing is expected when we have Outlook 2007 and above which does not cache message references (hyperlinked images in our case). Reason behind this is an expected behavior is Outlook 2007 and above versions do not keep the reference data of message/email body. The time it points to references data from specific location which is mentioned in hyperlink, which is nothing but advanced HTML content which renders based hyperlink. Unless the entire content is downloaded Outlook.exe will wait, once entire content is fetched in email Outlook.exe process will respond back. So the hang that is experienced is moreover an expected behavior when we have such advanced HTML content. This behavior with advanced HTML content is known to Microsoft since product is designed to wait until the content is loaded 100%.

Symptom:

Outlook contacting server for information when replying/forwarding/printing emails with HTML content.

Cause:

This is a known issue when you are dealing with HTML emails which have the images on a different server and are not embedded images.

When you open HTML emails which have images that are stored on another server Outlook will contact the server to download the images every time you open the Email. It won’t save it locally as the image is not a content of the Email. The emails only have links of the images which is actually on another server.

So when you forward or print Outlook will contact the server once again which ultimately will take some time to download the images.

In Outlook 2010, default and the only rendering engine is Word, and since Word is not a browser each image is considered separate from any other (a unique link). This is unlike a web browser which treats images like a pool of resources and will reuse the same one over and over if two tags share the same link path. So whereas a browser only needs to pull the image once, word will pull it for every image. In addition, word don’t guarantee rendering of content designed for web pages and not email.

Reading the email is OK because we can download images in the background (it is a synch). But to forward or print, we have to pull the images synchronously because we need the download to complete before we can proceed to the next step. So the reason it only occurs on those steps is by design.

Resolution:

This is a by design issue.
We have listed a few workarounds below:-

Options:

Uncheck the option in Trust Centre “Don’t download pictures automatically in HTML e-mail messages or RSS items.” which you have already tried and it is working for some emails but not all.
You may create a Registry Key as mentioned below which gives you the same behavior as the first step:

HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Common

Dword: BlockHTTPImages

Value: 1

You can open the Email in Web Browser by opening the Email and going to Actions -> View in Browser.
In Outlook 2010, under File tab, Options, locate: Replies and forwards: there is the option of four ways of forwarding email:

Fix:

File -> Options -> Trust Center -> Trust Center Settings -> un-tick the ” Don’t download pictures automatically in HTML e-mail messages or RSS items.

My sysadmin has been bugging me about this for months. Two or three users have been bitching about Outlook (2007 with an Exchange 2003 backend) asking for the username and password over and over again.

My sysadmin is now on leave and the MD is having the issue. Time to start looking into it. After a couple of hours searching on the web, I came across this article.

Go to – Control Panel – User accounts – Advanced – Manage Passwords

In here i could see my sysadmin’s accounts credentials against the mail server in questions from a couple of months ago. I clicked “Remove from Vault”. Issue fixed.

Should stop my Sysadmin bitching for now.

In Outlook, when you want to invite people to attend a meeting or event, you usually send a meeting request. The recipient can then accept the request and the item is added to his or her calendar.

There is an alternative method that works more broadly with Outlook and other calendar programs. An Internet calendar (iCalendar) attachment or a link to an iCalendar file can be added to the message body. When the recipient opens the attachment or clicks the link, the event is added to his or her calendar program. The link can be text or an image such as a button.

Note    Unlike Outlook meeting requests, when using iCalendar attachments and links you do not receive confirmations when people accept or decline.

Step 1: Create an appointment

If you already created the appointment on your calendar, skip to the next section, Step 2: Send an iCalendar attachment.

1. In Calendar, on the Home tab, in the New group, click New Appointment.
2. In the Subject and Location boxes, type the subject and location information.
3. Enter the Start time and End time.
4. On the Appointment tab, in the Actions group, click Save & Close.

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Step 2: Send an iCalendar attachment

1. On your calendar, click the appointment.
2. On the Appointment tab, in the Actions group, click the down arrow on the Forward command.

3. Click Forward as iCalendar.

A new message window appears and an iCalendar is attached.

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Step 3: Add a link to the message body

The link can be text or any image that you choose.

Do one of the following:

• Add a text link to the message body
• Add an image link to the message body

Add a text link to the message body

1. In the open appointment window, right-click the iCalendar .ics attachment, and then click Save As.
2. Select a location that all of your recipients can access.

For example, within an organization, you can select a shared network location. The most common scenario is to save the iCalendar .ics file to a website. Remember, when selecting a place to save the file it is important that any recipient has access to that location.

3. Click Save.
4. Click in the message body.
5. On the Insert tab, in the Links group, click Hyperlink.
6. In the Text to display box, type the text that you to appear as the link.
7. In the Address box, enter the location where you saved the iCalendar .ics file. If you saved it to a website, enter the Web address or URL (Uniform Resource Locator (URL): An address that specifies a protocol (such as HTTP or FTP) and a location of an object, document, World Wide Web page, or other destination on the Internet or an intranet, for example: http://www.microsoft.com/.) for that location.
8. Click OK.
9. Continue to complete the message as you normally would, including adding recipients, and then click Send.

Add an image link to the message body

1. In the open appointment window, right-click the iCalendar .ics attachment, and then click Save As.
2. Select a location that all of your recipients can access.
3. For example, within an organization, you can select a shared network location. The most common scenario is to save the iCalendar .ics file to a website. Remember, when selecting a place to save the file it is important that any recipient has access to that location.
4. Click Save.
5. Click in the message body.
6. On the Insert tab, in the Illustrations group, click Picture.
7. Click the picture you want to insert, and then click Insert.
8. Click the inserted image.
9. On the Insert tab, in the Links group, click Hyperlink.
10. In the Address box, enter the location where you saved the .ics file. If you saved it to a website, enter the Web address or URL (Uniform Resource Locator (URL): An address that specifies a protocol (such as HTTP or FTP) and a location of an object, document, World Wide Web page, or other destination on the Internet or an intranet, for example: http://www.microsoft.com/.) for that location.
11. Click OK.
12. Continue to complete the message as you normally would, including adding recipients, and then click Send.

Sample button images

You can save these sample button images on your computer and then use them when inserting an iCalendar link.

1. Right-click the image, and then click Save picture as.

Note    The command name might differ depending upon the Web browser installed on your computer.

2. Select a location on your computer, and then click Save.

Ref: http://office.microsoft.com/en-us/outlook-help/create-an-add-to-calendar-link-in-an-email-message-HA102114161.aspx#_Add_a_text