When trying to forward or reply to an email, Outlook 2007 gives this message:
Automatic Picture Download
To complete this action, Outlook must download content from a server other than your e-mail server. This could verify to the sender that your e-mail address is valid and increase the amount of junk e-mail you receive in the future.
Basically, what this means is that not all of the email was downloaded, and it’s asking you if it’s ok to download the rest of it (pictures) from someone else’s email server so it has the full email to reply to or forward.
Why this can be bad is if the pictures it’s trying to download are from a previous email in the chain – it will essentially let the company know that your email account (address) has connected to their email server to download those pictures. They could then use your email to spam you.
If you don’t trust ALL of the people in the email chain or don’t want the people hosting the picture content to risk getting your email address, click cancel then copy-paste the contents of the email into a new email. Otherwise it’s safe to click OK.