Allow vendor to send mail as client domain.

Hi Experts,

One of my client has below requirement.

1) User send an email to client domain. Say mail address is
2) Client is using EOP. When mail hit EOP, I created a rule to forward, that mail to another domain (Client vendor domain). Example Domain name is:
3) Once vendor receives that mail, vendor replies to that mail, as So, user can see that mail, as it is coming from not from
4) As vendor is spoofing client address, mails are getting blocked or going to spam.

In short, requirement is to allow vendor to send mail as client.

If anyone performed, such task in their environment. I am open for all options. Even creating new domain for client. If more info needed, let me know.
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AmitIT ArchitectAsked:
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Kent WSr. Network / Systems AdminCommented:
You can accomplish this with an SPF record from the SMTP server of
Whatever their SMTP servers IP is, add it to an SPF record (Usually TXT),  in the DNS server for
Make sure to add the ip4 and ip6 if the SMTP server has both.
This "allows" the's SMTP server to send mail on behalf of
AmitIT ArchitectAuthor Commented:
Thanks for the reply @Kent W

Do you have any document or url, which can give more details.
Kent WSr. Network / Systems AdminCommented:
Yes, the url I included would be a great place to start, but an example SPF record would be - (make sure to include the quotes if entering as a TXT record:

"v=spf1 ip4: ip6:2607:f0d0:1002:51::4 ~all"

The ip6 is only needed if their SMTP server also has ip 6 address.
Of course, change the IP address('s) above to reflect their actual ip4 / ip6 addresses of's SMTP server. If they have more than one server, you can add it with another ip4: statement or just do a range (ip4: It's safer to name them individually, though.

I suggest using the ~all (soft fail) at the end as opposed to -all (hard fail), especially while testing, so mail will make it through if there is another technical issue.

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AmitIT ArchitectAuthor Commented:
Thanks Kent. Enjoy your weekend.
Kent WSr. Network / Systems AdminCommented:
You too Amit. Hope it works for you.
Jamie McKillopIT ManagerCommented:
If the emails are getting blocked because of SPF, the domain already has an SPF record. Be careful that you modify it correctly to include the new permitted sender IPs and not disturb the list of IPs and/or hostnames already in the record. If the domain also already has an SPF record, the easiest way to modify the record for is to use the include parameter. You would add to the record. This allows all systems in the SPF record to send as the domain. This makes management easier if the sending servers in the domain change. They only need to be updated in the abc,com SPF record instead of both records.
AmitIT ArchitectAuthor Commented:
thanks James, i am planning to create a new domain altogether for vendor. As client don't want to make any changes in parent domain.
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