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My organization is currently outsourcing email delivery to an SMTP service provider. We're considering bringing that back in house to deliver our own emails.

We send about 5k transaction emails per day in relation to order confirmations and shipment notifications. This kind of volume and the importance of these emails means that we need to make sure our mail server is configured as best possible to avoid the emails looking like spam.

The emails we send tend to be similar in that they are templated order confirmations so the risk is that the emails are classified as spam and we get blocked or our emails bounce.

With the outsourced email provider, we get good deliver-ability, but if we did it ourselves, we're worried that emails won't get delivered.

Our ideas so far include:

  • Setting up reverse DNS correctly
  • Setting up SPF records
  • Domain keys (not sure if this is easy or difficult)

What are the tips & best practice to set up a mail server which can send email of this volume and avoid being classified as spam?

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Consider registering with dnswl.org. There are also a few open services which will verify your configuration.

  • Definitely get rDNS right, and use a subdomain for the host. eg. mail.example.com not example.com. Ensure you have a proper static IP address which is not listed with spamhaus.org. Avoid using any part of your IP address in the DNS name.
  • Match the mailserver name configured in your software to the DNS name.
  • Do setup the required postmaster and abuse email addresses.
  • Ensure callouts for the sender addresss works, at least for the target server.
  • Consider implementing Bounce Address Tag Verification (BATV) to allow verification of bounce notices.
  • Definitely do SPF correctly. While spammers use it, it will help prevent spammers from using your address. Also do SPF for the server. See the FAQ at open http://www.openspf.org/.
  • DKIM will authenticate the signed contents which may be useful for your purposes. It doesn't have much impact on spam scores. I am finding that a lot of the existing signers have broken implementations.
  • Do setup appropriate policies for email being sent and received. Implement as many of these in the server as possible to limit incoming email.
  • Limit the servers you relay for to those inside your LAN which need to send email. Only accept email for your domain.

I have a post on Running an Email Server with some other comments. Its a bit of a rant as several legitimate posters send email that looks very much like Spam due to poor email implemenations.

EDIT: Typically services like smtp, mail, and www have service related names (sub-domains). In some cases these will have numerical suffixes like smtp2 or www1. This makes it simple to provide the services on different servers simple. The servers usually have their own hostname (sub-domain) which is unrelated to the sevice(s) they provide. These days the domain may be used for web traffic, but is is often immediately redirected to the web sub-domain.

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  • Thanks for the helpful info. It's been a few years, but could you clarify why you suggest using a subdomain (mail.example.com) for the email host? It seems to be a common convention, but I can't seem to figure out why. Thanks.
    – Dominic P
    Apr 25, 2014 at 22:42
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    @DominicP If you don't use a sub-domain, you risk tying your email server to your web-server's IP address. For a small site this may not be an issue, but as you grow it becomes a problem. Also, spammers frequently use the domain they are pretending to send from as hostname in the HELO message. This is one of the factors that can be weighted in a Spam score.
    – BillThor
    Apr 26, 2014 at 1:44
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I'm assuming these emails are going to many different recipients at many different domains based on order information, status, etc., correct? So for any given external domain you might be sending just a few of those 5,000 emails? If so, then you should be fine. Just because you're sending a large volume of emails doesn't make you any more prone to being flagged as a spammer then a company that sends only a few dozen emails a day. Amazon.com sends hundreds of thousands of order related emails every day. Corporations that have thousands or tens of thousands of employess collectively send hundreds of thousands of emails a day. IBM, Microsoft, GM, and Walmart are all examples of corporations that send hundreds of thousands of emails every day.

If you follow the generally accepted "rules" for sending email, such as making sure your server is not an open relay, having valid rDNS and SPF records, etc. you'll be fine.

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SPF and DKIM won't reduce your chances of being labelled as spam as they simply show that you're authorised to send mail for a given domain (even spammers use SPF and DKIM).

Reverse DNS is the main one, as well as having your server HELO properly, and making sure that you're sending from a "proper" static IP address that isn't on any of the RBL's that list things like residential/dynamic IP blocks.

Of course, making sure you stay off any RBL's is the number one thing, but if you are just sending shipping/order notifications you shouldn't have any issues of your mail being unsolicited.

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  • Just wondered, how do you know this stuff, are there any guidance websites or books out there on this subject?
    – anotherguy
    Sep 21, 2010 at 21:35
  • I don't know of any real resources, it's really stuff you pick up just from looking after smtp boxes for a while. One good resource is the Postfix documentation simply because it does most of the best practise stuff so you'll see the options in the documentation - even if it does relate to Postfix configuration you can apply most of it to any smtp server.
    – flooble
    Sep 22, 2010 at 16:10
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Just a note that GoDaddy.com supplies a bogus rDNS entry for it's virtual dedicated servers (ip-XXX-XXX-XXX-XXX-secureserver.net) which is often flagged as a spam-producing type of address. GoDaddy will NOT change this (I've asked a few times, pointing out to them the flaws in their approach). So, thumbs down for using GoDaddy for hosting and email server.

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Email delivery handling is maintenance intensive. First option would be to use External SMTP Relay service providers (like this. If you do want to maintain the SMTP Server in-house, you can take this Email server test and implement given recommendations.

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