God, yes. Gmail, in particular, really enjoyed just dropping connections from my IPv6 addresses every few months. Sometimes it would return an error, something obtuse and wrong like maybe, "your forward and reverse DNS records do not match" even though they absolutely did and hadn't changed in years.
Outlook/Hotmail was far better and would always return a sane, yet sometimes inscrutable, error that bore some resemblance to reality. It still took them a week to get me off the hit list that I got dropped on for no discernible reason.
> Or they decide to mark your mail is "suspicious" and it goes into the recipient's Spam folder.
Gmail was the ABSOLUTE FUCKING WORST about this. My spouse's e-mail to Etsy customers who used Gmail--not spam, not newsletters, person-to-person e-mails INITIATED BY THE CUSTOMER--would work for the first couple of e-mails in a thread and then start going into spam. Or, even more fun, friends with whom either of us had e-mailed would send us a mail and then we'd reply and nope, into spam.
Gmail would do this for WEEKS and no amount of poking or begging or pleading would make it stop. And then it spontaneously would. So maybe the begging did work but was just delayed. I dunno. I tried signing up for Gmail's "Postmaster Tools" but no data was ever reported because "your mail volume is too low."
The ultimate ignominy? The final humiliation that sent me to Fastmail? I finally, through a couple of professional contacts, got to actually e-mail (via Gmail, of course, because they were blocking my personal domain again) with a real, live Gmail SMTP admin to ask why my latest round of e-mails were going into the bit bucket. Know what he said, even though my domain has been hosted on a server in the same colo facility with the same IP addresses for a decade? Something along the lines of "your domain reputation is coming back as too new."
Ladies and gentlemen, I give you whois:
google.com - Creation Date: 1997-09-15T04:00:00Z
mypersonaldomain-notreallythisvalue.org - Creation Date: 1997-03-10T05:00:00Z
That is fucking shameful indeed. Domains with tiny volume need postmaster tools the most…
But it seems like having a little conversation from your domain with a gmail address helps. Just send a mail to your google account, click not spam, reply, do a couple more back and forth replies.
Worst of all, the mail does not always bounce... and when it does, this is no one to email and ask. What are mail admins supposed to do?
Did you follow up on that crap and asked what the fuck could possibly be going on with this nonsense? (More politely than I just did of course.)
I did your exact follow up - politely and persistent!!
It was a dead-end. They had no idea - and worse - no escalation path to the SMTP team.
You can have a domain registered with Gmail or Rackspace Mail or whatever, and use the SMTP credentials they give you for outbound, while keeping MX records point to your own SMTP for inbound. Or you can let them process the inbound as well (fighting spam for you) and you just forward everything (or sweep via IMAP) and put it into your own Dovecot.
This way you control what's important to you (email storage/backups/etc) but outsource delivery and spam filtering.
I tried this with Mailgun, and it caused my mail to be marked as spam.
That's only if your broker and doctor are not using Gmail or G Suite, otherwise your email (with them) is likely to be read by Alphabet regardless of your server setup.
[0] https://www.bloomberg.com/news/articles/2017-06-23/google-wi...
It sucks ass when your mail does not get through as GMail/Hotmail rejects a connection from the IP address your cloud company allocated for you, in spite of DKIM etc. Or they decide to mark your mail is "suspicious" and it goes into the recipient's Spam folder. Fighting these huge hosting companies is impossible as they don't want to talk to you.
Also constant tweaking Spamassassin is not fun. My setup worked well for for the first four years but then started letting more crafty junk through... So, I had to compromise by moving the mail to Fastmail.