What You Need to Know About Your Mailing Infrastructure and Deliverability

If you send your email marketing newsletters in-house, then it’s important to have a mail server that is set up correctly since a poorly configured server is a telltale sign of being a spammer.  Not sure where to even begin to ensure that your system is set up correctly? Below is checklist of some of the key items that ISPs check before accepting a connection from another email server.

Email format – Ensure that your emails are RFC (5321 and 5322) compliant.

A Record – Ensure that your sending (sub)domain resolves to an IP address(es) by creating a DNS A record. The IP doesn’t have to match your sending IP address. In fact, lots of companies list their web site’s IP address instead.

PTR Record – Ensure that each of your outbound IP addresses resolve to a hostname, or a Fully Qualified Domain Name (FQDM). Use meaningful names that match your sending domain, rather than dynamically generated ones. If you plan on setting up feedback loops, it’ll help if you’re sending (sub)domain is listed in the hostname. For example, if you send email from news.xyz.com, then your IP may resolve to a hostname, called mta1.news.xyz.com, rather not mta1.xyz.com. Many ISP FBLs require proof of IP ownership. This is one of the easiest ways to comply with this requirement.

Blacklists – Ensure that your sending IPs and URLs are not listed on major blacklists.

HELO – Ensure that the name of your sending server matches that of the hostname listed in the PTR record.


  • SPF Compliant Sender ID record – Ensure that your sending (sub)domain listed in the From: and Return Path: email headers have valid SPF records (v=spf1). Sender ID (spf2.0/pra) is no longer required.
  • DKIM – Authenticate your sending (sub)domain with DKIM. It is unnecessary to authenticate your emails with DomainKeys if it is already authenticated with DKIM.
  • DMARC – This is the latest hot topic in the email industry. Click here to learn more about it. Return Path also offers a free online tool to help you create a DMARC record.

Don’t have an open relay or proxy – Ensure that your outbound servers  are secure and aren’t vulnerable to bad actors that would send their spam from your servers. Use such as www.checkor.com or www.mxtoolbox.com/SuperTool.aspx to see if your servers are an open relay. Getting a connection  refused, time out, unauthorized host, or denied result means that you don’t have an open relay.

Sending limits –Do not bombard the ISPs with too many emails at once. Adhere to their recommended sending rate guidelines, most of which are listed on their Postmaster site.  Return Path offers a Connection and Throughput Guide to help ensure the proper settings are in place.

What other mailing infrastructure checks do you find to be important in reaching the inbox?  Leave your suggestions in the comments below!

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