14 DAY TRIAL // Since it was first released, Gmail was available as a private beta and every user who was interesting in obtaining a new account could do it using an invitation provided by Google. At this time, even if Gmail is available for free for all the users, we are all able to send no less than 100 invites to other Internet consumers. However, they can represent an easier way to create new Gmail accounts for your friends so many people found them very useful. That's why some of the users encounter several difficulties with the invitation system, most of them appearing when they try to send the message.
As the Gmail Help Center sustains, most reports inform the parent company that the invitations didn't reach their destination and the invited users were not able to register for a new account.
"If you've lost an invitation because it went to the wrong address or because the recipient doesn't want to use it, you can resend the same invitation by retrieving it from your 'Sent Mail.' Forwarding a previously sent invitation to another email address will enable the new recipient to create a new Gmail account, as long as the original recipient did not use the invitation. Please note that each invitation link has the capability to create only one account, and expires three weeks after it is first sent."
The bad thing about the invitations is that the search giant will not replace the lost ones but some new invitations will be soon offered to some of the users. "If you've lost an invitation because of technical issues, we're sorry to say we can't provide you with a replacement. However, as we make progress with our service, we will continue to issue a small number of new user invitations to a randomly selected group of Gmail users."