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Comments
Spot on!
To me it looks like most of the ISPs that don't do it at this point are in third world countries. They get heavily blacklisted as a result. Every ISP should do this, it would smash botnet activity worldwide to a fraction of what it is and no one runs a mail server at home because residential ISPs don't let users set reverse DNS (an absolute requirement, though some offer it with business packages, at which point they could unblock 25).
I can request that from my ISP (the second largest in my country), but only if I have a static IP. Setting up a static IP costs a one-time fee of 10.00 EUR plus a monthly fee of 2.00 EUR.
A static IP (which includes the option to request rDNS setup) was free until recently, and I think there is no change for customers who requested it in the past.
From what I read on local forums, most ISPs here can set up rDNS on request under their own conditions.
Yes, I get your point here. However, I believe what I think @jar was trying to say is that most ISPs don't offer rDNS for residential customers. This is generally true, except in some cases where static IP addresses or business plans are involved, such as you have just mentioned.
Yeah, but I had a static IP with most of my old ISPs by default. At least in my country, dynamic IPs have only become common in recent years. So even as a residential customer, requesting rDNS wasn't really an issue. If you wanted it, you had it. The only difference now is that you need to pay for a static IP address.
As example (via google translator) they started to charge for static IP since 1 August 2022.
https://www-t--2-net.translate.goog/novice/napoved-obracuna-staticnega-ip-ja-za-rezidencne-uporabnike?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp
If you have a dynamic IP, port 25 is closed along with NetBIOS ports. If you have a static IP address, port 25 is open, but NetBIOS ports are closed. A business plan is not required for a static IP, but you now need to pay a fee. It was free until recently.
Even still, there's no good reason to value that for port 25 delivery when better can be had at so much better value. Good email relays are not expensive... SES? A random residential ISP's IP ranges that aren't their direct emails servers aren't likely to have any reputation value. At bare minimum it's taking a really weird detour for such an allegedly normal use case.
But for all the time I spend looking at reverse DNS records I'm pretty sure the overwhelming majority of residential IP space is not forward confirmed and I doubt a second hand renter of it is getting that authority to set one. I believe I could concede to a relatively minor exception while still being satisfied with my conclusion.
OP is probably trying to utilize RCPT TO probing to verify email address during SMTP transaction
Interesting. That would actually match the claimed use case of "email verification". I figure the residential connection would be to fool google into thinking the request would actually originate from a human and not some automated list washing tool or whatever.
Edit: Well, that doesn't make sense either as then OP wouldn't need port 25... What's the advantage in doing that from a residential IP besides a higher chance of being blocked? I don't get it.
I'm a bit north-west from where you seem to be located and 99% of all end user IPs have been dynamic here since like the 90s. Granted there probably were/are options to get static ones with the bigger ISPs, which i've never tried so i'm not sure if you'd need a straight up business contract or paying some premium is enough but the average user doesn't even know about that let alone would consider ordering those. Static IPs (maybe even with the possibility of setting reverse DNS) among end user ISPs around here can probably pretty safely measured in per mill at best.
Maybe ‘verifying’ SMTP logins from a credential dump, but that also would not need 25 specifically
Yeah, it's mysterious... He likely could just conveniently run those against submission/POP3/IMAP/..., which probably aren't blocked about anywhere.
The only situation where i'd feel that a residential IP would make some sense is if he doesn't know about submission and wants to blast a bunch of emails through the SMTP server of some email provider, while making sure that the headers show the original source to be residential (or if the provider in question blocks DC IPs from connecting to SMTP in general but is there any relevant ones that do this?).
Kind of, but not really... Many ISPs that block outgoing 25 have an open email-relay for their customers to use, however, it is only for their customers (IP space), not everyone.
Yes, of course, but it's a relatively easy option to have rDNS for residential customers too (at least where I live, that is some 500km away from you :-). That's what I said.
How many people actually use it, I wouldn't even guess. Most likely much, much less than in the days when running things at home, experimenting, and especially IRCnet with cool looking vhosts were still big things around here.
My ISP is clear about that. If I pay 2 euros monthly, I can have a static IP without port 25 blocked and with rDNS available. Before August 1, 2022, we could request a static IP free of charge.
The problem with this approach of email verification
Also, if you do not implement one secret thing, mail servers may "lie" to you
But yes, it is possible to achieve what you want.
For this, you need cloud servers with 25 port open and random IPs, instead of proxies.
As you might put a lot of IPs to spamhaus.
So you think it's actually about list washing? How would the residential part make sense there though?
No other use cases.
He probably tried and found that many cloud providers block ports or require compliance validation of the mail program.
Yeah, probably and then someone told him that residential proxies would be the magic bullet so off to LET he went... Well, at least something along those lines.
A first post, necro post and product shill all in one. This has to be a record!
Guess I should have just flagged without commenting!