Ask HN: What reliable SMTP service to use for low volume emails (~500 p/m)

I am currently using SendGrid, but the deliverability of messages is around 85%. It seems that if you use their free plan, the IP addresses used are shared between other free users and that opens up the possibility of abuse that affects all other free users.

Is there an alternative solution that gives close to 100% deliverability? (paid or free).