In fact, I'd say it's getting easier, not harder. There was a time when fairly arbitrary rules were applied (like "thou shall not send email from a dialup IP Address). They seem to have mostly gone now, and when they are still in place you can just self report via a web form you are not being naughty and it's all good.

But you do have to keep your nose clean. Do not send SPAM, under any circumstances. Sounds easy, and indeed it is easy if you are just running a mail server for an organisation where all mail you are sending is generated by people within that organisation. But if you are doing something that involves relaying emails, eg something like running a mailing list, it becomes harder.

To give an example - I run a mail server for a club of maybe 20 people. All email is strictly policed, eg you have to sign up, all sign ups are reviewed by a human, including any email asking to sign up. All good right? Nope, because the club has to have at least one email address (say for the secretary) that does not involve signing up. Those emails are all moderated of course - but you are notified of emails waiting for moderation via email. Those notifications contain snippets of the original. If one of the moderators has a GMail account, those snippets triggering SPAM filters can get your server banned by google. The solution is to run a imap server for secretary@ and get them to fetch it manually. Bypass Google for all relayed email in other words.

So you have to follow the rules and it's not always obvious what you have to do to follow the rules, but it ain't impossible, and in fact once you know what the rules are it isn't even hard. Any capable sysadmin could do it.