www.anoncraigslist.org is an email-based service which anonymizes your email address and phone numbers your reply email before it’s sent to the posting party in real-time.
Real email addresses and phone numbers are written normally in the body of the reply email. The sender simply adds “anon” infront of the craigslist domain name (i.e., firstname.lastname@example.org becomes email@example.com.) Then during the email transfer proces all of the senders known email addresses are replaced with anonymized versions and all phone numbers are replaced with anonymized versions.
The person receiving the response never sees the senders real email address or phone number in the body of the email, yet can contact via email or by phone as usual.