Change or spoof outgoing SMTP server name

smtpwindows-server-2008-r2

Having a strange problem here.

We send out emails from a web application that use an SMTP server setup on a Windows 2008 R2 server.

Everything was working fine but one of our customers changed their incoming mail program (that's the best I could get out of their IT department) and now they're rejecting all our emails.

They did some digging and said that they're getting rejected because of non-alphanumeric characters in our originating server name.

Emails originating from our SMTP server come from MACHINE-NAME.DOMAIN_NT.abc. They've told me it's the underscore that is doing it.

Now they asked us if we could change our domain name which of course isn't happening. Another solution would be to relay through another server but that's going to be a pain.

I was wondering, can I spoof the domain name so the originating server will be MACHINE-NAME.DOMAIN.abc or something that doesn't have the underscore?

Best Answer

Go to IIS 6 Manager from Administrative Tools, then expand your server, then right click the SMTP Virtual Server and select properties, then click the Delivery tab, then click the Advanced button, in the "Fully-qualified domain name" field type in the name that you want the server to identify itself as.

Related Solutions

How to fix an “invalid” SMTP server issue

This probably has to do with not having public reverse DNS records set up for the server sending the mail.

Check that you have set up a reverse DNS record for your server, and that the address it reports to send from (after any SNATting, etc) can be resolved and reports the correct domain of the sending server.

Linux – How to correct Postfix’ ‘Relay Access Denied’

TLS just enables encryption on the smtp session and doesn't directly affect whether or not Postfix will be allowed to relay a message.

The relaying denied message occurs because the smtpd_recipient_restrictions rules was not matched. One of those conditions must be fulfilled to allow the message to go through:

smtpd_recipient_restrictions =
    permit_sasl_authenticated
    check_recipient_access hash:/etc/postfix/filtered_domains
    permit_mynetworks
    reject_unauth_destination

To explain those rules:

permit_sasl_authenticated

permits authenticated senders through SASL. This will be necessary to authenticate users outside of your network which are normally blocked.

check_recipient_access

This will cause postfix to look in /etc/postfix/filtered_domains for rules based on the recipient address. (Judging by the file name on the file name, it is probably just blocking specific domains... Check to see if gmail.com is listed in there?)

permit_mynetworks

This will permit hosts by IP address that match IP ranges specified in $mynetworks. In the main.cf you posted, $mynetworks was set to 127.0.0.1, so it will only relay emails generated by the server itself.

Based on that configuration, your mail client will need to use SMTP Authentication before being allowed to relay messages. I'm not sure what database SASL is using. That is specified in /usr/lib/sasl2/smtpd.conf Presumably it also uses the same database as your virtual mailboxes, so you should be able enable SMTP authentication in your mail client and be all set.

Best Answer

Related Solutions

How to fix an “invalid” SMTP server issue

Linux – How to correct Postfix’ ‘Relay Access Denied’

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