Installing too many add-ins can make Outlook slow too.
Solution – To find out if add-ins are causing a problem, start Outlook in safe mode and see if it performs better. However, if it does, go into Outlook’s Trust Center and disable any suspected add-ins, then restart Outlook normally.
Problem 5 – Outlook PST has corrupted You’ll know if your PST has corrupted if you start seeing errors pointing out the same on opening Outlook.
A corrupted PST can lead to inaccessibility of all data within your Outlook since it won’t allow it to open.
It eventually reaches to such an extent that working with Outlook becomes nearly impossible due to its utterly slow speed.
Find out the folder called “Larger Than 100 Kb” in Outlook 2007, it will contain all emails that are larger than 100 Kb.
Delete all unwanted old emails (especially the ones with bulky attachments).
If you really need an attachment, save it to the disk but clear it out of the PST.
Also, delete all other unwanted emails and clear out the Trash.