We have all e-mail blasts going out and relaying off level 3. This has pros and cons.
My only advise would be to ensure the addresses you are sending to are valid if not you will receive a lot of back scatter(NDR) which will get you blacklisted by level 3 quickly not to mention the other BL'S out there.
Have you tried SMTPget and Digitalaka™ for sending bulk emails. I have been using both of them for the last 14 months and had no issues with issues. I have sent 1 lakh emails per day easily and they give good configurations like:
1. Dedicated IP address
2. SPF & DKIM
3. DMARC records
They ensure that your emails directly reach your customer inbox not marked as spam.