Contacts gem and mailing solution to handle email bounces


My app has a feature to import contacts from gmail,yahoo and hotmail. I am using CONTACTS gem to achieve that. The functionality is working fine, I can import many contacts in bulk. I also have a "invite your contacts" feature as well. Issue arises here: Quite a few of the invite mails fail when we send the invitations to them. When this happens in large scale ie many people inviting their friends using web import and invite feature, bounces can go high in number. I am concerned about rated as spam guys.

1.What is the solution to handle these bounces.

2. Not so important, but still wanted to seek suggestions for this :if anybody is using such feature, how are you handling the queues of such invite mails. if 100 people invite 100 others then we have, 10000 mails already. Which itself will take 7-8 hours to handle. If the user base grows then , time taken to handle the chunk will grow as well. Any suggestions?