Apr 10th, 2018
Create invalid email address against that domain.
e.g. domain : example.com Email Adddress : firstname.lastname@example.org, email@example.com
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 18.104.22.168... 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: <firstname.lastname@example.org> Response: 250 2.1.0 OK z79si2772641pfi.381 - gsmtp
Step 5 - Target email address which you want to validate
Command: rcpt to: <email@example.com> Response: 250 2.1.5 OK z79si2772641pfi.381 - gsmtp
If you got
ok for invalid email address then that domain is catchall domain.
When a user registers with their email account, a unique link is sent to said account and the user is asked to click on it to confirm the registration process.
This double level process allows you not only to eliminate invalid email addresses but it also helps to prevent situations where a user can register with an email address that does exist, but does not belong to the given user.
The double opt-in technique also prevents spam users from registering with fake accounts.
It is a very effective way to ensure they type their email correctly. Double typing allows users to avoid typos or syntax mistakes.
Using just this solution itself is that spam users can still provide you with an email that they don’t own.