I can't speak for outside the UK, but here the ISPs hand out non-static[1] IP addresses to residential customers. These IP ranges are in the spam-block lists that a lot of the other mail providers use. As such sending any email directly from your ISP given IP address is hit-and-miss affair. You don't even get any bounce notifications, the emails just disappear and never arrive at their destination, so you have no idea that something is wrong.

Some ISPs allow you to pay for a proper static IP to get around this problem, but again some of the ranges are still in the block lists. The only way I could guarantee that my IP wasn't blacklisted was to switch to a business account with my ISP and thus have IPs from a different range.

If you are stuck on a non-static IP, the easiest way around the problem is to send via the SMTP smarthost that your ISP hosts.

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[1] They are technically dynamic IPs, but are sticky in that you keep the same IP unless your router goes offline for more than a couple of hours.

In my personal experience, it was certainly a problem for a while when lists like SORBS and their notoriously hostile de-listing procedures were all over the place. Listed an entire IP block assigned to a data center I had hardware in as "residential" and it took weeks to get it addressed.

And more recently, I'm still unable to send email to Verizon.net email addresses from a VPS because they too insist it's in a residential IP block. (it's not.)

For the first few weeks I had a VPS and moved a small business to it, sending anything to Gmail was a hassle as it was all automatically going to the spam folder. The typical responses from others was "find a new provider" even though checking blacklists showed the one I chose was just fine.

I too have run mail servers, and have seen enough to realize that it's definitely not a myth. It's just that there are enough spammers making a mess of things for the rest of us, which is unfortunate.

Same experience. Mostly fine to run your own server. I check the blocklist status of the IP before moving/setting up a new server.

We end up on Hotmail/Outlook's blocklist about once a year. They remove it within 1-2 hours after opening a ticket.

I lost $150 because a certain mail didn't arrive in time (an intercity bus trip ticket) when I couldn't actually afford to lose that money. I had to borrow money from a friend. Those 1-2 hours were quite valuable!

Running your own mailserver is easy enough if you have an IP that isn't blacklisted. Most residential IP's will be on the Spamhaus PBL which will cause issues. You can run a mailserver on a $5/month VPS without issue as long as you have a dedicated IP and you check for blacklist entries before you start.