Emails Letters and Mailing Lists-Turn on email links
From Support Wiki
Adding an attachment : Sending an email with a link that will display the attachment : Turn on email links
Turn on email links
When receiving an email that contains embedded hyperlinks (links), the recipient may have trouble accessing the links due to settings prohibiting these links within their own email program. Many email programs disable access to these links by default in an attempt to alleviate phishing threats from untrusted sources.
To successfully open an embedded email link, the recipient needs to turn on the access to email links, either temporarily for a single email or globally for all emails.
The instructions below are when using Microsoft Outlook 2003 or 2007 but other email programs may contain similar selections. Contact your email software provider for specifics related to your particular email program.