Excellent idea. We know even the exact type of companies, so should be easy to get the list.
Are you aware of any online service which can automate for us sending of sales letters and brochures? Something like sendgrid but for letters / brochures.
I researched this idea a while back and found that Vistaprint has the automated sending service. I don't think it'll have the API approach of Sendgrid though.
There's also a whole industry of fulfillment houses for direct mail, but in my experience they're pricey and very traditional in their approach (sales-people, couriered proofs, no/printed analytics reports etc).
If you're going to do this regularly you can save a ton of postage by signing up for a business account with the PO and pre-printing the envelopes in a special format (although I always wondered if hand-writing would boost the conversion rate).
Also, try postcards rather than letters as USPS postcard rates + biz account will let you get your rates down to < $0.20/mailing - but sales letters may have a far higher conversion rate depending on your product, making them worth the extra postage.
Are you aware of any online service which can automate for us sending of sales letters and brochures? Something like sendgrid but for letters / brochures.