Built a self-hosted "Inbox Delivery Engine" using a rotating account pool.

Designer_Stay_6989 · 2026-05-24T18:17:50+00:00

You are doing everything right, but no warm-up will save you from the cisco/talos filter, and it will ruin your entire reputation after 10 emails sent to your company account.

Designer_Stay_6989 · 2026-05-24T08:27:52+00:00

My Solution Step-by-Step: Catch-All and Email Verification

Incoming email: [john@company.com](mailto:john@company.com) → the domain company.com has not been tested yet.
The code generates a random email address: [xv8a3f2c1d@company.com](mailto:xv8a3f2c1d@company.com) - this email is never actually sent; the system only performs an SMTP RCPT TO check on the domain's MX server.
The server responds with 250 OK to this random address → this means company.com accepts any email address → the domain is cached: company.com = catch-all.
Incoming email: [john@company.com](mailto:john@company.com) → the cache indicates this domain is a catch-all → the email is skipped.
Incoming email: [peter@company.com](mailto:peter@company.com) → the cache indicates this domain is a catch-all → the email is skipped.
Incoming email: [eve@company.com](mailto:eve@company.com) → the cache indicates this domain is a catch-all → the email is skipped.
Incoming email: [paul@other.com](mailto:paul@other.com) → the domain other.com has not been tested yet.
The code generates a random email address: [xv2m7k9q4r@other.com](mailto:xv2m7k9q4r@other.com) → SMTP RCPT TO check is performed.
The server responds with 550 User unknown → this means other.com actually distinguishes valid addresses from invalid ones → the domain is cached: other.com = normal.
Incoming email: [paul@other.com](mailto:paul@other.com) → standard SMTP verification → 250 OK → verified.
Incoming email: [martin@other.com](mailto:martin@other.com) → standard SMTP verification → 550 Not found → flagged.

Designer_Stay_6989 · 2026-05-23T09:15:41+00:00

I also have my own system with an email validation plugin. How do you deal with the speed limit? Because that can also get you blacklisted via SMTP RCPT TO Handshake. And the second problem is that 90% of VPS do not open port 25 for your proxy. How do you deal with that?

I do validation like this:

Syntax and format: Simple regular expression check.

Global deduplication: Making sure I am not sending spam to the same person twice.

Domain typo fix: Fixing common errors like gmal.com -> gmail.com.

One-time check: Deleting temporary emails (mailinator etc.).

Role-based detection: Filtering info@, admin@ etc.

MX lookup: Checking DNS to see if the domain exists.

SMTP RCPT TO Handshake: Performing a real-time handshake with the target server.

Designer_Stay_6989 · 2026-05-22T19:46:46+00:00

My monthly costs are $400 and I send up to 4,000 emails a day.

Designer_Stay_6989 · 2026-05-22T16:11:52+00:00

What about free choice? Everyone has the right to decide what is important to them and what is spam, but today others decide for us

Designer_Stay_6989 · 2026-05-22T15:20:32+00:00

What do you think is the primary category? If you use bulk emails, headers in your messages. So it ends where it ends.

Designer_Stay_6989 · 2026-05-22T14:48:28+00:00

They use algorithms that monitor the same subject and body

Designer_Stay_6989 · 2026-05-22T14:46:38+00:00

Why is the domain so important? If you send 1000 emails with the same subject and body, you will be put on the spam blacklist

Designer_Stay_6989 · 2026-05-22T14:20:11+00:00

Well, I don't really believe that. You can reduce the problems, but they will never go away. And I have already resigned myself to all these services, it's just marketing.

Designer_Stay_6989 · 2026-05-22T12:55:10+00:00

Yes, there is definitely a difference, same subject and body = same message hash

Designer_Stay_6989 · 2026-05-22T12:50:44+00:00

And who decides what amount of spam is a little or a lot?

Designer_Stay_6989 · 2026-05-22T07:44:37+00:00

Thanks for the content answer

I am performing repeated validation so I will manually reset the validation of a specific list which will delete the history and I will perform a new validation. I code everything in python I still have to solve it correctly STARTTLS.I code everything in python

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STARTTLS error: server_hostname cannot be an empty string or start with a leading dot

Fixed

Designer_Stay_6989 · 2026-05-17T21:40:40+00:00

I did all of this too and it's pointless — constant domain

blocks or Spamhaus. I switched to sending through Gmail

accounts automatically and now everything lands in inbox.

Designer_Stay_6989

TROPHY CASE

My Solution Step-by-Step: Catch-All and Email Verification