We require that sponsors use a bonded mailing house when emailing to attendees because the Eclipse Foundation's Privacy Policy requires us to keep the personally identifiable information private. Email addresses are personally identifiable information and thus we cannot release email addresses to sponsors.
Using a bonded mailing house is a standard technique for sending an email message to a list without revealing the email addresses. (1) The sponsor sends the email contents to the bonded mailing house; (2) the Eclipse Foundation sends the email addresses to the bonded mailing house; (3) the mailing house does the mail merge and sends the email; (4) the mailing house discards the addresses.
We cannot send the email addresses directly to a sponsor nor to a sponsor's internal marketing department nor to an online bulk mailer that does not have a "do not reveal email addresses" option.