I actually clicked this thread after reading the first part of the article, and saw that the author has already made 3 very important points (in ASCII bullet points) that I came here to say basically the same thing. All of this is extremely important in terms of real world outbound mail deliverability.
>Do not cheap out on providers. Run your mailserver in the most reputable IP space you can find. Most likely you will use some type of cloud instance or VPS (probably in such a way that the line between the two is blurry). Unfortunately, per-month cost tends to correlate directly with IP reputation quality, as does name recognition. But neither are any guarantee. AWS has plenty of IP reputation problems. Sometimes a little-known, brand-new VPS provider can be a surprisingly good option because they got their IP space off of some staid corporation that maintained an impeccable security program. Do some research to try and find out what kind of results people get from different providers.
> From an IP reputation perspective, consistency is key. Mailservers and IP reputation are like credit cards and your credit report: once you open one, you want to keep it as long as possible so that it will build a good IP reputation. Do not move your mailserver around between providers to save money, it will result in headache.
> Do not run a mailserver off of IP space that is not intended for commercial services. For example, running a mailserver on a residential ISP is a terrible idea (if it even works, many residential ISPs drop outbound on port 25). You will be guaranteed to have IP reputation problems and, moreover, IP space allocated to end-users usually gets reported to a "policy block list" such as the one Spamhaus maintains... meaning your outbound email will be blocked by recipients simply because it's coming from an IP that should not have mailservers, so it's most likely to be from a compromised end-user device.
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Now to add my own 2 cents:
If you are serious about doing this, find a medium sized long-established ISP where it is still small enough that you can get in contact with the people who run the routers. And that ISP should be one that really cares about its IP space reputation.
If you can afford it, anywhere with long-held IP space belonging to its ASN that has never had $5/month VPS customers on it, or any form of shared hosting environment, is much more likely to have "clean" IP space.
I'd recommend looking around locally in your city/region. Lots of cities have small, well-established companies that do a grab-bag of MSP, IT, Microsoft hosting, and offer some VPS or colo. They're usually on the expensive end but they come with the benefit that they've usually had their IP space for a long time and manage it carefully (unlike basically any "modern" provider), and since they're in town it's usually easier to get someone on the phone if there's a problem. Make friends with the people who run these kinds of businesses anyway, in a lot of smaller markets especially there's a bit of an informal club of IT service providers and if you chat with them regularly you'll end up getting good advice and business leads. I've had a colo inquiry to a local company turn into them sending me one of their clients before just by being chatty with the network guy.
Won't be cheap but most of the colocation service providers listed here, will sell you 1U-2U of rack space and DIA/IP transit for a self hosted mail server.
Don't have to connect to the SIX or have an ASN, just buy default routes from somebody with a presence near the "core" of the internet in Seattle. I'm using the SIX page there as a handy list of westin and westin-adjacent colo providers.
>Do not cheap out on providers. Run your mailserver in the most reputable IP space you can find. Most likely you will use some type of cloud instance or VPS (probably in such a way that the line between the two is blurry). Unfortunately, per-month cost tends to correlate directly with IP reputation quality, as does name recognition. But neither are any guarantee. AWS has plenty of IP reputation problems. Sometimes a little-known, brand-new VPS provider can be a surprisingly good option because they got their IP space off of some staid corporation that maintained an impeccable security program. Do some research to try and find out what kind of results people get from different providers.
> From an IP reputation perspective, consistency is key. Mailservers and IP reputation are like credit cards and your credit report: once you open one, you want to keep it as long as possible so that it will build a good IP reputation. Do not move your mailserver around between providers to save money, it will result in headache.
> Do not run a mailserver off of IP space that is not intended for commercial services. For example, running a mailserver on a residential ISP is a terrible idea (if it even works, many residential ISPs drop outbound on port 25). You will be guaranteed to have IP reputation problems and, moreover, IP space allocated to end-users usually gets reported to a "policy block list" such as the one Spamhaus maintains... meaning your outbound email will be blocked by recipients simply because it's coming from an IP that should not have mailservers, so it's most likely to be from a compromised end-user device.
===================
Now to add my own 2 cents:
If you are serious about doing this, find a medium sized long-established ISP where it is still small enough that you can get in contact with the people who run the routers. And that ISP should be one that really cares about its IP space reputation.
If you can afford it, anywhere with long-held IP space belonging to its ASN that has never had $5/month VPS customers on it, or any form of shared hosting environment, is much more likely to have "clean" IP space.