We recently had a client who lost all their emails – every single email – because they never cleared out Outlook and kept all file attachments received and sent within Outlook. The outlook data file (.pst) grew to over 2 Gigabytes in size and then the version of Outlook they were running just blew up and corrupted the file. There are a host of tools on the market that can fix this, but don’t let yourself get into that position in the first place: when attachments come in save them in a proper file directory structure within My Documents, and don’t save copies of all Sent emails in Sent Items: write a rule to forward them to yourself instead, so they pop back in your inbox. From here you can file them by the relevant customer, delete attachments etc.
Regularly (every couple of months) check your Outlook file size (right click on Outlook Today and select properties), and if it’s getting big use advanced search to find any objects over 1MB and then reduce them in size (save the attachments locally, or if there are large images embedded within the email then right click, edit the message, remove them and then save). Then repeat for items >512k and >256k. Having done this clean out, empty your deleted items, and compact the file (properties advanced). You’ll be left with a smaller file, quicker to load and not likely to just blow up in your face one morning!
PS. Whilst you’re at it have a quick look where your Outlook file is actually saved and make sure this is in your backup path: you don’t want to have a problem then reach for your backup and find the file isn’t in there after all (you do backup every day – right?)