Bulk email represents one of the largest portions of legitimate email (spam is not included in this category). Sending bulk email requires a lot of bandwidth, and technical expertize to obtain high delivery rates. Newsletters that you are subscribed to, are typically sent via newsletter management companies, such as Vertical Response, MailChimp, Constant Contact or iContact. It is also expensive, with $10,000 per year to manage a 100,000 mailing list (including mailing, unsubscribes, reporting, A/B testing, resolving issues with ISP's and blacklisting services such as Spamhaus, and so on).
What if Gmail, Yahoo mail and Hotmail (they account to more than 60% of email addresses targeted by bulk email) offered the following services to make bulk emailing less bandwidth-consuming, and easier to monitor. Any time you send a newsletter to more than (say) 50,000 Gmail recipients, here is how it works:
This achieves the following goal: Gmail actually distributes the message (not you), using Google servers that are close to their Gmail servers. There is also one fewer node between the sender (the mailing list management company) and the recipient, thus saving considerable bandwidth. In short, it benefits both the sender, Gmail and the recipient (the latter one benefits thanks to better monitoring capability by Gmail, to block a message when deemed spammy).
There is a problem: what if you send a customized email to 50,000 recipents? For instance, the message starts with "Hi [Your Name]". The workaround is simple: Gmail could accept a few macros in your message, such as [Your Name], and deliver the customized version to all 50,000. All is needed is a very rudimentary macro language. And of course, the mailing list uploaded on Google servers must contain the email address but also the first name., for this type of customized message.