I use the free tools as well, but most of the folks I consult for, I also administer their mail account server @ Google or Microsoft, so I can keep an eye on both sides of the transaction. Implementing SPF/DKIM/DMARC/smtp-tls also helped keep things clean. You can register as a postmaster @ AOL, Microsoft & Google, and also get reports if something is reported as spam.

A well behaved remote mail server should either reject/bounce the message, or deliver it to a user's spam folder, it should never just drop it. Unfortunately, It's near impossible to determine if your message ended up in a user's spam folder :(

My server sends 50-100 messages a month, tops, and I never send mass messages, just direct messages to family, friends & customers. The biggest issue I had was when Rackspace periodically (+ voluntarily) reported their VPS IP space to Spamhaus, which required me to inform Spamhaus that I was responsible for that specific IP, and it should not be on the blacklist.