Outgoing Mail SMTP Server. Five Simple Ways To Set It Up Right and Not to Become a Spammer

How many letters you send every day with your outgoing mail SMTP server? One hundred? Perhaps one thousand?

You use bulk mailing to communicate with your customers, to send newsletters and commercial proposals and it is an integral part of your business

In this case, sometimes you face “your-e-mail-can’t-be-delivered” problem. It is normal, when 5-10 messages out of a thousand can’t be delivered (of course if you have a clear, healthy and well maintained subscriber list).

Now what will happen, if 10-20% or even all of your messages never reach their destination? This nightmare may very well realize, if somebody classified you as a spammer.

Nowadays almost 90% of all sent emails are spam. Therefore, it is not surprising that everyone tries to avoid spam. Providers create much stricter anti-spam filters. In turn, filters are trying to block as much mail as they can, sometimes blocking your legitimate business correspondence.

You are very upset when this happens. Let me try to help you make anti-spam filters your friend and help you configure your own outgoing mail SMTP server in such a way, that they will recognize your letters from afar and treat them as old friends.

First of all, let’s take a look at the diagram below. It describes the basic steps, which your message makes when you are emailing.

Of course I am presuming you have a healthy, totally legal opt-in list and your message does not classify as spam. If not, these rules will not help you that much.

To achieve this we need to observe five simple rules. These rules were invented to check your messages before they are delivered to recipient's mailbox. Anti-spam filters are built on “assigning trust”. If something looks suspicious, they will decrease your trust score and if it is decreased enough, your letter will sink into oblivion forever.

Here is what you have to do when you run your own outgoing mail SMTP server, or when you are going to start bulk mailing:

Get your own Static IP address
Configure forward & reverse DNS resolution
Check black - lists
Configure SPF
Configure Domain Keys (optional)

Perhaps these items seem a bit alien to you, but in fact, they are quite simple. Let’s analyze them.

Get your own static IP

Most, if not all of your regular Internet providers will not give this to you by default. You are usually assigned with a floating (dynamic) IP address and this IP changes every time you connect to the Internet. This is like shooting a moving target and most email servers will block you if your connection comes from such a dynamic IP. So first priority of the day for you would be to call your provider and get a static IP from them.

Forward & Reverse DNS resolution

Another mandatory rule for your local outgoing mail SMTP server – you must take care of is configuring forward & reverse DNS resolution. DNS resolution occurs when a client queries a name server to obtain the IP address with which it wants to establish a connection. If a name server in the local domain cannot resolve a client’s request, it queries parent servers to locate a server that can.

They can create a form of authentication showing a valid relationship between the owner of a domain name and the owner of an IP address dedicated to the email SMTP server. While not very thorough and definitive (you can still forge it), this validation add a lot to your trust score, since spammers and phishers usually do not toil with it or would not want to show their real name to anybody.

They tend to use stolen or temporarily hijacked domains and IP addresses, and no provider will agree to register a domain without some form of ID (like credit card). So, it is just an additional way to find you by your domain name if you go bad and start spamming.

At the diagram below you can see the ways server use DNS resolutions.

Forward & reverse DNS resolutions proceeds with the help of so-called A and PTR-records. Don’t forget to add these records in your DNS – just ask your provider or domain registrar to do this. These records in your DNS are used for implementing DNS look ups and will help you work on the Internet openly. Therefore, you will be more trusted with different servers and spam filters.

For example, your IP address is 125.42.17.10 and your domain looks like “mail.bob.com

your A-record looks like “mail.bob.com A 34.54.65.23”
your PTR-record must looks like “34.54.65.23 PTR mail.bob.com”.

Please note, that if you set an “A record” of your domain name in your DNS, this does not mean that your Internet provider configured the back-resolve (PTR) record for your domain automatically. Sometimes they do, sometimes they don't. At least make sure you check it with them. Also, the IP address of your outgoing mail SMTP server must be resolved back to the same domain from which you are sending your emails. Recipient's servers do check that a lot.

Black - list

DNS blacklists or DNS block-lists are the lists of IP addresses, that are stored in remote database and are accessed with the use of DNS query. They are used to block IP addresses, that are suspected or potentially send spam. Mail server will check the existence of IP-address of the client, from which it receives the message. After the positive response the message is detected as spam will be blocked.

Here you can see what is happening with your email when it is checked with black list

Sometimes (not always), the receiving email SMTP server sends you an error with the cause of failure. In general, when you find out the reason, you can check with blacklist site, most of the time it contains instructions on how to remove your IP from the list.

SPF

SPF is not a “sun protection factor”, as you might think. SPF is the next useful DNS record. It indicates hosts that have the right to send emails for a specific domain. SPF is used to verify whether source IP of the sender is allowed to relay messages for this domain. If you are sending an email from the IP that is different from the specified – the server may reject your email or tag it as spam.

SPF record is optional and it will help you show your good intentions to the receiving server. If you decided to use this type of DNS record - visit the site, which knows everything about SPF - openspf.org. If you are going to setup SPF – ask your domain registrar. Some of them have special wizards in their configuration panel, which can help you to setup your SPF automatically.

Domain Keys (optional)

There is additional verification standard, that is not used as widely. It is debatable if it will help or not, because only a few select providers do check it..

Domain Keys was created to identify the sender of email messages. Very similar to SPF it added cryptography to ensure that only a person, who has the right key, can send a certain email.

As you can see Domain Keys does not filter spam itself, but if you show a correct source domain, filtering mechanisms can work more effectively and will not mark you messages as spam.

We came to an end. Now you can see that paying attention to such trifles helps you to act as openly as it is humanly possible.

This is especially useful when you are going to create your own outgoing mail SMTP server, it will help you avoid trouble with the spam filters – they trust senders who specified most complete and visible data.

These five rules are not so difficult as they seem, and following them might be quite easy and very rewarding indeed. So don't forget to check: