That's simpty not true. We never ever do send spam, and i mean not even newsletters for our customers. And i still had problems when delivering invoices (PDF attachments), And thats with paying mxtoolbox 25$ to monitor blacklists. The biggest problem was microsoft365 mail service. We then switched to external local mail provider (europe) that had better delivery but even then some of the invoices would simply get stuck in microsoft365 and i would get no reponse. We are now using mandrill, and it works ok. I did not want to host it outside of europe but i did not have any other option.

One anecdote against another. My suspicion is that you were in a "bad neighbourhood" - ie. using a hosting or email service that didn't keep their IP's squeaky clean. AWS/EC2 is a common host among the HN crowd but is one of the worse places to host a own mail server at for this reason - they'd also rather upsell you SES than fix the EC2 IP ranges' reputation.

Microsoft is the pickiest email provider to get good delivery rates to - they require a gradual volume ramp-up over 1-4 weeks on a fresh IP to see it as good, in my experience, and SNDS is something to keep a close eye on during that time - it clearly indicates your IP's reputation with them and how much mail they see from it. That number being higher than expected plus the sample emails they provide may indicate something going wrong - through this, I once discovered an obscure feature in a software package I used that allowed visitors to send emails to arbitrary addresses.

Mandrill has better delivery than the other email services I've tried but is cripplingly expensive for a hobby project that happens to have a nontrivial userbase.

> My suspicion is that you were in a "bad neighbourhood" - ie. using a hosting or email service that didn't keep their IP's squeaky clean.

No, not really, we are using one the most expensive offerings in Switzerland. Renting dedi servers for spamming would be not only extremely expensive, they would kick you right away if they noticed. As i said we did nothing wrong, used monitoring and our invoice emails would sometimes end in the spamlist for microsoft, after trying to get it right i gave up and hooked mandrill.

if you are runnig some random internet forum, some part of your notifications ending in spam is not a big deal, but for us, invoices ending in spam box is not something you can ignore.

I remember I had to go through a couple of hoops with outlook.com and gmail(?) using some un-/under-documented web sites to get "approved" (sending a mail, getting a reply, typing reply in web form).

And in my experience the major services have unpredictable spam filter behavior.

I even saw Google being cute and assuming mail in Japanese was spam - because my profile is western.

So yeah. If your goal is 100% (not high 90s) deliverability - including the odd big attachement or foreign encoding mail - it's not trivial.

Thankfully I don't care that much if a recepient at Gmail or outlook don't get my mail;it's their fault. If it's a problem the recipient should move to a more reliable mail provider.

It's obviously not as easy for commercial/work mail...

Reputable only matters when small. When large like aws you could be getting anyone's ip.

AWS has a vested interest in upselling you SES for email-sending needs. The quality of their EC2 IP ranges has little to do with their size; running a tighter ship with those IP's is merely bad for their business model.