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We have a smtp server for sending email ,but recently we found that when we send hundred of newsletter to * at a short time, it will blocked them. any one have better solution to solve it ? Thanks in advance!

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migrated from Aug 26 '09 at 13:18

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It seems that Yahoo recognises spam when it sees it. – pavium Aug 26 '09 at 13:12
"we found that when we send hundred of newsletter to * at a short time, it will blocked them" -- But it's opt in! He swears! – Dave Drager Aug 26 '09 at 13:38
Are there any errors in your logs from when they blocked it? – Bill Weiss Aug 26 '09 at 15:30

12 Answers 12

up vote 6 down vote accepted

Are you following Yahoo's Best practise guidelines as seen here? Also, have you filled in the form here?

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They key here is "within a short time." If the IP you're sending from is unrecognized and doesn't have a "reputation" built up yet, then many of the server providers will throttle the number of messages they will accept from you over time. Some suggestions:

  1. Send from an IP that has an established reputation. You can use tools such as SenderBase to check on yours and look for problems with your reputation.

  2. Limit the number of messages you send at once. Instead of blasting out hundreds or thousands of messages at once, trickle them out over several hours.

  3. Practice proper list management. Track your bounces and failures. Make sure that invalid addresses get removed from the list. The providers will penalize you if your percentage of invalid delivery attempts gets too high, or if you repeatedly try to deliver to the same invalid addresses over and over again.

  4. Ensure your messages comply with the CAN-SPAM Act (assuming you're mailing within the United States). Don't use misleading subject lines, include a physical mailing address, provide an opt-out and make sure it works.

  5. Target your list. Instead of using a shotgun approach and sending all mail to the entire list, segment to target those who would be most interested in your content.

  6. Ensure all technical issues are properly addressed, such as reverse DNS, SPF records, DKIM, abuse and postmaster mailboxes on the sending domain, have an contact record, etc.

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Can't emphasize SPF records enough. I used to send out bulk mail (try 700k and more in one sitting) and SPF records are a must as is a trusted IP address. – Techie Joe Oct 8 '13 at 23:18

General problems with sending mail (either high or low volume):

  1. No reverse IP address set. Make sure you have a reverse PTR entry set on your IP. Check with dig -x IP.ADDRESS
  2. IP must be static and non-residential.
  3. Your IP or range of IP addresses around you are in a blacklist database, either internal at Yahoo or other services such as Spamcop. Check on a site that checks multiple databases, such as
  4. SPF records not set for the domain you are sending from.
  5. You are not sending from an IP that has been "approved" or "known" as a friendly, non-spamming email server.
  6. The words of your "newsletter" are spammy and Yahoo recognizes them as such, and blocks based on volume and that. Generally an email generates a score based on 1000s of attributes, some are good and count for you, and some are bad and count against you.
  7. A number of Yahoo users have marked your message as spam, so it disallows you to send more of that same message to their servers.

I think that is about it - hopefully you are not "spamming" and this is some sort of double opt-in list and also it is CAN-SPAM compliant.

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Could be a problem of sending domain authentication


The Problem: Sender Address Forgery

Sender Policy Framework


DomainKeys Identified Mail

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I hate to be the one to tell you this but you are going to run into constant issues with getting email delivered. As time goes on some individuals will mark your emails as spam, which will get your ip address listed as a spam source. You ability to get email delivered will get worse and worse.

I recommend that you outsource email delivery to a company such as or (there are several more good ones). These companies will manage your deliverability for you and remove this immense headache from your life.

Good Luck

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You can setup a feedback loop with yahoo to check your emails are not taken as spam by your recipients.

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I have seen this behavior with Yahoo in the past. They do greylisting so when you start sending much email to them it starts getting delayed. I have seen email delayed for up to 72 hours in the past. As Zypher pointed out they have a form to register for bulk email. Probably your best bet is to use a service like mail chimp to do your bulk mailing.

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You're likely sending from a residential IP block. Does your ISP have a gateway SMTP server you should be using?

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When the users registered for the newsletter, you should have sent an email confirmation to them. This way, as long as people don't mark you as spam, you will be an established contact, so to speak. Since you have already had an email correspondence with these people, Yahoo is less likely to block your mail. If there was no prior communication, Yahoo will assume that a bulk mailer is spam. Also, certain key words in your message will flag the spam-blocker.

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If you are legitimately sending bulk email to yahoo the have a form (go to contact at the top they won't let me directly link) you need to fill out so that your email doesn't get blocked by their anti-spam system.

If you have DomainKeys and SPF setup you can get feedback from them on who is marking your newsletter as spam so you can remove them from your mailinglist pro-activly to avoid hitting their spam threshold again.

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Consult the Yahoo Postmaster site.

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If you are using Mailman to deliver your newsletters, you might need to configure your SMTP_MAX_RCPTS setting in the file.

At the bottom of the file, type:


This will batch the number of messages sent to one domain at a time, if I recall correctly. By default, the number is 500, I believe. We had problems delivering to Hotmail until we knocked this number down.

You can go even further if you like.

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