The idea of having them send an e-mail to an address containing their IP is clever, however you need to authenticate that the person who sent the e-mail is either somebody who queried your site, or somebody that got the address from somebody who queried your site or else you could just figure out how to generate that base64 yourself and impersonate somebody else’s IP address which could have catastrophic results if you then fed these IPs into something like a block list and suddenly you’ve blocked Microsoft/Office 365. To be fair, I doubt anybody is going to try and reverse engineer one person’s code to then figure out how to impersonate who sent spam, but if this became a widely distributed program you could just pull off Github then it would be more concerning.

A couple ways to solve this:

1. Sign the information before encoding it in Base64 so you can verify it came from your site and wasn’t just spoofed. This has the upside of being stateless since you don’t need to keep a record of every e-mail you’ve generated but comes with the disadvantage of spending CPU time signing the text which could be exploited as a DDoS.
2. Spit out a random e-mail address and record which e-mail address was given to each IP. Presumably you wouldn’t hold on to this list forever since IPs change owners frequently and so an IP that was malicious 1 month ago could be used by a completely different person now and so you can trim this list down once a month to avoid wasting disk space. You’d probably also want to keep some amount of these requests in memory (maybe 10Mb or so) to avoid ruining your IOPS.

All this said, I think your time is better spent with the using unique e-mail aliases as the author suggested but with 2 changes: 1) use aliases which are not guessable to prevent somebody from making it look like somebody else was hacked (e.g. me+googlecom@ gets compromised, but the spammer catches on and sends from me+microsoftcom@ instead to throw off the scent) and 2) don’t use me+chickenjockey@, use chickenjockey@ or else the spammer can just strip “+chickenjockey” from the address to get the real e-mail address.

Eh it depends. I’m fortunate enough to be in a good IP block so I don’t get my e-mails dropped purely on that. It’s been a good learning experience and I’ve leaned on my own server a number of times for troubleshooting at work since I can see the whole mail flow. The only problem I have is the free Outlook/Hotmail will not accept my e-mails. Everybody else seems fine. All that said, I don’t host anybody else’s e-mail so I haven’t had any spam come out of my IP, and I would never in a million years host e-mail for a customer.

The spam filtering is painful. I kinda work around it by giving a unique e-mail for everything and of one starts getting spammed I just rid of that e-mail. Tends to give you advance warning of data breaches too since you’ll start seeing the spam come in before the announcement.

It’s a colocated server. I provided the physical server and they put it into a rack in a datacenter with power and networking (static IP).

If this works out it might be a nice place to migrate to away from my self-hosted e-mail provided they eventually let you bring your own domain. Just sucks that e-mail is essentially the most secure thing you need to have since compromising that can compromise every account attached to the e-mail. That’s a lot of trust you need to instill in your e-mail host.

This forced account shit is infuriating. I’d see students with computers that cannot get to government-provided education sites because they are forced to sign up with a Microsoft account to use their PC, which forced them to setup a child account because of their age and therefore be under a parent account, which means the child account can only use Edge and can only go to whitelisted websites, which blocks some government education sites unless the parent account allows it through which they can’t until the student goes home.