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Dave Cousineau
Asked: 2022-03-03 14:44:55 +0800 CST

Meaning of "sender"?

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Reading documentation about SPF records, I can't quite seem to disambiguate the meaning of "sender". It could mean "the IP where the mail client sent the message" or it could mean "the IP of the mail server that the mail client is contacting".

So, it could be my home/business IP address (where my mail client is), or it could be just the address of valid mail servers.

email email-server spf

3 Answers

  1. A "sender" in the SPF record is the IP address of the computer which tries to send the email. In other words, when an SMTP server checks SPF, it will check against the server which is currently connected and is trying to send the email.

    So you need to include the IP address of your SMTP server in the SPF record, and not the IP of your client.

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  2. You can specify it by IP or by hostname in your DNS zone according to this documentation:

    An SPF record is a DNS record that has to be added to the DNS zone of your domain. In this SPF record you can specify which IP addresses and/or hostnames are authorized to send email from the specific domain.

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  3. Best Answer

    My understanding now is that it's actually the last SMTP server before being delivered, which may be very different from the SMTP server your email client contacted. So it is definitely not your mail client's address, and likely may not be your first SMTP server's address either.

    This will mean that you need to determine the full list of your provider's server addresses. This can be a very large list of addresses, and so there is likely some kind of "spf" prefixed domain offered by your provider that can be included in your spf record instead of listing specific addresses or even address ranges. Eg:

    v=spf1 include=spf123.mymailprovider.com ~all

    This allows your provider to update their record as necessary and for you to have the lastest changes automatically.

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