How to detect if domain has catch all policy to accept email?

Question

I am almost done with a tool to detect if email is valid or not. I am stuck at small point where I have to detect If mail server or domain has catch-all policy enable.

C

Answer 1

You can identify domain is catchall or not by using Telnet. Create invalid email address against that domain.

e.g.
domain : example.com
Email Affffdress : dummyemail@example.com, invalid.email@example.com

How to Telnet:

Step 1 - Find mail exchanger or mail server of example.com

Commmand : 
nslookup -q=mx example.com

Response:
Non-authoritative answer:
example.com mail exchanger = 10 aspmx.l.google.com.
example.com mail exchanger = 20 alt1.aspmx.l.google.com.
example.com mail exchanger = 30 alt2.aspmx.l.google.com.
example.com mail exchanger = 40 aspmx2.googlemail.com.
example.com mail exchanger = 50 aspmx3.googlemail.com.

Step 2 - Now we know mail server so let connect to it.

Command:
telnet aspmx.l.google.com 25

Response:
Trying 74.125.24.27...
Connected to aspmx.l.google.com.
Escape character is '^]'.
220 mx.google.com ESMTP z79si2772641pfi.381 - gsmtp

Step 3 - Enter helo hi

Command:
helo hi

Response:
250 mx.google.com at your service

Step 4 - Email address from which you telnet to targeted email address

Command:
mail from: 

Response:
250 2.1.0 OK z79si2772641pfi.381 - gsmtp

Step 5 - Target email address which you want to validate

Command:
rcpt to: 

Response:
250 2.1.5 OK z79si2772641pfi.381 - gsmtp

If you got "ok" for invalid email address then that domain is catchall domain.

A catch-all domain in simple terms means, the server of that company will catch any email sent to that domain, even a non-existent address and store it in a section called the catch-all. When this happens, you have no clue if it’s a legitimate email address or not.