Edit: We can at least keep using our servers for incoming mail, and just use those for sending.
For me, it wasn’t Gmail. It was Proofpoint and Microsoft. During a very email-critical time I couldn’t get emails out to certain Proofpoint customers or to Hotmail.com addresses (specifically). And it was important enough for me to switch rather than try to fix.
Microsoft was likely arguably fixable but Proofpoint wanted me to prove ownership and control over the entire IP allotment from which my mail was emanating in order to lift the restriction on my single IP. That wasn’t possible because I didn’t control the entire space my IP was in.
It’s become increasingly difficult to operate email independently without a lot more money and time at the least. This worries me.
We had almost no issues with Gmail, only with Outlook "Protection"
Google kills a lot of the bigger ecosystem.
(Not to mention lack of basic features. I've got a laptop at some point and wanted to synchronize read status between my devices. I ended up writing NNTP to Maildir converter so I can use my IMAP server for this. Not pretty.)
Additionally, the linked post explains that if you get flagged as spam or "sending to many emails" there's literally no way to fix it without sounding the alarm in a post like this.
Unsolicited marketing email is a problem, and I don't think we send anything that a reasonable person could categorize as that. We send
-replies to user support requests
-new vehicle listing alerts that users have explicitly signed up for (eg by running a search for a car on autotempest and then entering their email address in the "get alerts for this search" field)
-monthly newsletter, again with explicit opt-in only
And I send a handful of personal B2B emails.