As I understand, transactional email is often triggered by a user itself (new account creation, forgot password, etc). By definition, those are sent spread out over time.
This is - at least from a spam filter's perspective - a huge email broadcast, more akin to a news letter mailing or a spam run.
And semantics aside, a lot of those 43M users will consider the email to be unsolicited (didn't remember they signed up, don't care about computer security, etc). They will happily report such an email as spam, adding to the training set.
This is - at least from a spam filter's perspective - a huge email broadcast, more akin to a news letter mailing or a spam run.
And semantics aside, a lot of those 43M users will consider the email to be unsolicited (didn't remember they signed up, don't care about computer security, etc). They will happily report such an email as spam, adding to the training set.