This script checks if a smtp server accepts a certain email address or not. This might be useful, if you for example have a custom domain and create unique email addresses for each site you sign up. Some email services have a delay until the new mailbox/alias becomes active after creation.
You could just wait a while and hope the mail address is ready when you sign up on a site. But why not verify to see if it is actually valid. You could use a website like https://emailchecker.info/ but why using a service that may collect each address you type in? You can also use telnet, but that is a lot more typing.
Lookup what the MX servers for a domain are
dig mx gmail.com
Check if the address exists
telnet gmail-smtp-in.l.google.com 25
Trying 2a00:1450:400c:c08::1b...
Connected to gmail-smtp-in.l.google.com.
Escape character is '^]'.
220 mx.google.com ESMTP t14-20020a05600c198e00b003c6f3e3eb7bsi1322386wmq.135 - gsmtp
ehlo foo
250-mx.google.com at your service, [2a02:908:176:3bc0:69d6:3800:17de:b489]
250-SIZE 157286400
250-8BITMIME
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-CHUNKING
250 SMTPUTF8
mail from:<foo@gmail.com>
250 2.1.0 OK t14-20020a05600c198e00b003c6f3e3eb7bsi1322386wmq.135 - gsmtp
rcpt to:<foobar@gmail.com>
250 2.1.5 OK t14-20020a05600c198e00b003c6f3e3eb7bsi1322386wmq.135 - gsmtp
quit
221 2.0.0 closing connection t14-20020a05600c198e00b003c6f3e3eb7bsi1322386wmq.135 - gsmtp
Connection closed by foreign host.
The code comes from https://gist.github.com/arulrajnet/c613bd0fad5de00bab2e plus some small modifications for python 3.
python MXEmailVerifier.py -e foobar@gmail.com
2022-10-24 13:50:45,373 - EmailVerifier - INFO - Parsed Email id : foobar@gmail.com
2022-10-24 13:50:45,382 - EmailVerifier - DEBUG - MX host is gmail-smtp-in.l.google.com
2022-10-24 13:50:45,634 - EmailVerifier - DEBUG - VERIFY 252, b"2.1.5 Send some mail, I'll try my best o12-20020a05600c4fcc00b003b4cb9ebdb5si5724930wmq.181 - gsmtp"
2022-10-24 13:50:45,654 - EmailVerifier - DEBUG - FROM 250, b'2.1.0 OK o12-20020a05600c4fcc00b003b4cb9ebdb5si5724930wmq.181 - gsmtp'
2022-10-24 13:50:45,796 - EmailVerifier - DEBUG - RCPT 250, b'2.1.5 OK o12-20020a05600c4fcc00b003b4cb9ebdb5si5724930wmq.181 - gsmtp'
2022-10-24 13:50:45,796 - EmailVerifier - INFO - foobar@gmail.com, True, b'2.1.5 OK o12-20020a05600c4fcc00b003b4cb9ebdb5si5724930wmq.181 - gsmtp'
Run the docker container and provide the email address as an option
# providing no option uses the default from the CMD option in the Dockerfile
docker run -it --rm --name emailcheck mschirrmeister/mx-email-verifier:latest
# provide the email via "-e <email.you.want.to.check@example.com>
docker run -it --rm --name emailcheck mschirrmeister/mx-email-verifier:latest -e foobar@gmail.com