[doubled112]

And sometimes if you do everything right, it still doesn’t work.

Recently I checked the IP against blacklists, waited a few months, did all of the other things, and then found out Microsoft bounces my entire VPS’s IP range. Appealing did not help.

They intermittently block Cloudflare email routing IPs too. All of these security measures and still it comes down to the IP address of your sender.

[1over137]

Is it an el cheapo VPS?

[doubled112]

Is Cloudflare a cheapo VPS?

It is a cheap VPS, but it would still be nice if there was a way to know (not assume) beforehand.

> 550 5.7.1 Unfortunately, messages from [IP ADDRESS] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150).

> Your IP(s) qualify for conditional mitigation.

Still blocked. The system is working as expected.

[inigyou]

Cloudflare is one of the shadiest hosts around, almost as bad as the big three clouds.

[TZubiri]

You can't have the cake and eat it too.

Either you use cheap infrastructure that attackers can buy by the bulk for sybil attacks.

Or you pay a reasonable price for a slice of an IP block that doesn't share its reputation with elcheapos.

[doubled112]

No disagreement here. I had never planned to use it for email, but I was bored and I already had it when I got an idea.

[jeffbee]

I would simply like to point out that 550 at SMTP time is not a bounce.

[doubled112]

You get an email bounce back with an error code in it. Is there some other definition I'm unaware of?

Wait, that is probably from the local mailer, and otherwise the sender may never know about the rejected messages.

[b112]

5xx are bounces, a perm failure. 4xx error codes are temp (retry) errors.

[jeffbee]

Incorrect. A bounce is a delivery status notification generated by a mailer after it has already accepted a message for delivery. A 5xx permanent error is a refusal to accept the message in the first place.

[TZubiri]

Is this standarized terminology in some RFC like SMTP? Or is it presumably some well established folk lingo?