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I have a server that hosts several websites. Each website has is own newsletter cron.

I know that there are more important things (envelope sender, spf record, ecc..)

but i would like to know if the number of emails sent per minute and the email size are relevant for spam filters.

If they are relevant, are they related to the machine sender domain or the return path domain?

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  • You mean emails per minute being sent to the same recipient domain? Because my spam filter would have no idea how many emails per minute you send to other domains. – joeqwerty Jul 9 '14 at 15:09
  • Yes, I mean: I can't predict it (or it would be too much expensive to...), so in worst case lets considere that we are sending all emails to the same recipient domain... – nulll Jul 9 '14 at 15:20
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I would like to know if the number of emails sent per minute and the email size are relevant for spam filters.

Usually big email provider will take precautions to defer your email if your sending rate was above normal. Abnormal sending rate is a sign of spam outbreak. This pattern usually caused by hijacked server then spammer will send spam as many as possible for very short time. For example, see this question about sending rate to Yahoo.

As for email size, I don't have data to support/reject your assumption (email size affect spam filters).

If they are relevant, are they related to the machine sender domain or the return path domain?

Usually spam filter will blacklist the client IP address, because return-path-domain was easily forged. With that blacklist, you, as server administrator, will know that destination server doesn't like either your email content or your sending rate.

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Spam filters are usually "trained" to recognize certain mail items as spam rather than looking for volume or the size of the emails. While the amount of mail you send can cause some filters to question emails sent from your domain (i.e, what your mailserver's IP reverse resolves to), it's only a small part of the overall filtering.

If you're sending a high volume of junk that people mark as such, filters will learn to filter out the emails and report the IP address of the mail server to the appropriate DNSBLs.

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