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I need to check a list of about 40 000 mails if they are valid. I want to use this guide: http://www.labnol.org/software/verify-email-address/18220/ It works perfectly one by one but I am afraid that if I made a program that would check them all I could get banned mainly because it would be basically a dos attack.

What do you think? |Is there another way? I cant use any online service for that as I dont own the list of emails. Thanks

user3000140
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  • Where did you get these emails from? Do you have permission from the owner of the email server to do this testing? If you are testing a corporate email server as part of a job, then that should be fine. If you acquired a list of potential sales leads from a potentially shady seller, much caution is advised. – Robert Columbia Jul 11 '16 at 15:50
  • One of our clients imported lots of emails, many of which are old. I need to check them in order to prevent being banned from mandrill or mailchimp – user3000140 Jul 11 '16 at 15:57
  • I'm voting to close this question as off-topic because this is not a programming question. – Martin Smith Jul 11 '16 at 16:09
  • I think this is a valid question but I think it needs to be reworded to fit the scope of Stack Overflow, perhaps phrase it more as "I have this code (and show the code in the question) and want to use it to test 40k emails but don't want to get blacklisted, etc." . Explain your situation and if possible add a tag for the program you would intend to use for this. Then you can be helped with a program-specific solution. – Martin Jul 11 '16 at 16:19
  • What if the server is secure? Telnet'ing to port 25 won't work for those I bet. If you send one email per second it will take about 12 hours to have your answer. – dbasnett Jul 13 '16 at 00:36

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I cant tell you if you will get banned but the techniques I would use to avoid getting banned are

  • Use a public IP address, proxy or vpn (eg mobile internet, wifi hotspot, TOR) as if you do get banned it wont effect you
  • start slow, process 5-10/s at first and then speed up, if you get blocked by one server go back to your last known good speed and don't connect to the blocked server for a while, check if you are still blocked manually
  • depending on the connection setup speed, only do a few emails per domain at a time. ie do 1 @gmail.com, 1 @Hotmail.com and 1 @yahoo.com per batch this stops you flooding one email server with thousands of requests at a time.

Hope this helps

Topher Brink
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