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.

"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."

Is this new ? I have been part of discussions on HN about personal mail servers for ... 8 years ? This is the first I have heard someone mention registering their mail server with google ...

Search for "Google Postmaster tools" or check out

https://postmaster.google.com/managedomains

You don't have to register per-se, but you get access to reports for your domain so you can see any potential trouble.

Corporate email admins can be more aggressive and unpredictable than big ISPs or Google or Microsoft, because they have a more direct relationship with their fellow staff. They can train users how to manage their own whitelists, and they usually already have an IT helpdesk staffed answer questions and concerns from users.

Corporate email admins can also be opinionated about email senders because their email system is only for their employees' work, specifically. They are less likely than Gmail to care about email from the little guys who are trying to build an audience or business. They definitely don't see it as their job to provide startups and random people with access to the inboxes of their staff. They will err on the side of saying no to unfamiliar email.

Corporate email is where it gets hard. You can have a clean IP, all the authentication options configured correctly, and still struggle to get out of the spam folder. This is one reason businesses will pay for big-name email platforms, which have spent a lot of time and money building good reputations with corporate teams, and have people who specialize in maintaining those reputations.

I've noticed that a lot of corporations set up greylisting [1] for their mail servers. So that might be one reason why you are seeing a lot of bounces, and you just need to resend the email after a few minutes. I use SendGrid, which automatically handles this. But it's always annoying to get these bounce notifications.

[1] https://en.wikipedia.org/wiki/Greylisting

A useful tool is sender score: https://www.senderscore.org/lookup.php?lookup=0

Oh, good, I have an MX record. Glad somebody could confirm that for me.

The domain lookup info is silly, but if you lookup your smtp server IP it’ll show you a score that in my experience is correlated to the probability of it not being in a blacklist.

You can use rblmon.com to monitor IPs for inclusion in public blacklists. There are other SaaS alternatives in this space as well, in addition to self-hosted scripts/applications. Amazingly, RBLs are still a thing that people need to care about, after so many years.

Disclaimer: I'm one of the developers behind RBLMon.