configure iis6 smtp server to send from a specific IP

scim1971

10/26/23, 4:48 PM

We have a dedicated Windows 2016 server that hosts multiple websites. Each site uses the IIS6 SMTP server to send emails from the websites (enquiries, order confirmations, etc.) - each site has a unique IP address but messages sent from the server were always sent via the primary server IP. This IP was then used in the SPF records of the websites as being permitted to send emails on behalf of those sites. This has all worked fine for years.

Last week the hosting company moved/migrated/cloned our server to their new platform and now I'm having problems with the SMTP server.

Emails are now being sent out (via the SMTP server) using random (seemingly) IP addresses rather than the primary server IP - the IP addresses it uses are ones assigned to the websites on the server (i.e. from the pool of IP addresses assigned to the server). This means the emails are failing the SPF checks (as the sending IP is not specified in the SPF record) and getting bounced back. I spoke with the host who stated "...with the new platform, the server was created with 20 network adapters i.e., for each external subnet so that has caused issues with the outgoing SMTP" - this means I can't change the default IP address on the NIC as there are 20 NIC.

There are 88 IP addresses on the server so I can't add them all to the SPF record of each of the 87 sites.

I've tried setting all the IP's (except the primary server IP address) as "skip as source = true" but that caused server 500 errors when trying to send emails (I think it was still trying to access IP addresses that were set to skip).

What I need to do is tell the SMTP server to "send" emails from a specific IP address but all I can see in the configuration screens is how to assign an incoming IP - not an outgoing IP.

Is it possible to specify the outbound IP in IIS6.0 SMTP server?

I would really appreciate any help with this - the mailroot/queue/ directory is filling up with emails that are not being accepted by the recipients email systems because of the random sending IP address.

Thanks for reading.

164

0 + 2

smtp

iis-6

spf

windows-server-2016

Lex Li

10/26/23, 11:49 PM

The SMTP components have been deprecated, https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-r2-and-2012/dn303411(v=ws.11)#quick-reference-table so you shouldn't use it any more.

joeqwerty

10/27/23, 12:42 AM

Do yourself a favor and get an account at SendGrid, MailChimp, whatever, and use that as a smarthost for your IIS server.

Elon Musk

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EN: configure iis6 smtp server to send from a specific IP

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