I'm going to mention that at one point my company produced a custom product^, that cost 100's of dollars per purchase, and was only delivered via a single email

I'm going to mention that at one point my company produced a custom product^, that cost 100's of dollars per purchase, and was only delivered via a single email. We had those emails marked as spam on numerous occasions. To this day we have never sent a marketing email, or even non-transactional email - mainly because we suck at marketing, so it's not like they got confused about which email... ^ We do audio transcription, a customer sends an mp3 in, we have someone listen and type it up, and we emailed the customer the results. These days you can collect the transcripts from the website, but for years you couldn't.