Email Deliverability

What is deliverability?

It’s all very well sending off a bunch of emails, but in these days of spam filters and strong data protection, how can you be sure that your messages are arriving where and when they should? Well, that’s what deliverability is all about.

When email was first designed there was no need to be concerned that an email was really from the person who it said it was from, and that it contained what they really said, and everything was accepted. It was all very simple – you sent something, and some time later, it arrived.

With the rise of the internet, some people have taken advantage of this relatively weak system, and so we have spam. In order to combat spam, various systems have arisen to help allow legitimate messages through while blocking the unwanted ones.

How can we improve deliverability?

We mentioned in our data protection page that the only way to combat spam is with integrity. This amounts to playing the good citizen online, making sure that you fulfil all the criteria when it comes to the things that are going to be checked for on message delivery. Here is a list of things that a recipient’s mail server might check when you send it a message, and what measures can be taken to ensure safe passage:

Check	Measure
It’s coming from who it says it’s coming from, and not some impostor.	Message origin is currently best enforced by SPF, the sender policy framework. You place some information in your DNS server saying who is allowed to send email from your domain. Smartmessages can help you set up your SPF records.
It hasn’t been altered or tampered with since it was sent.	Message integrity is ensured with DKIM (Domain Key Identified Mail). We use cryptographic keys placed in your DNS to digitally sign your messages. Smartmessages can help you set up your DKIM records.
That it isn’t to an address that’s been previously rejected	Message sending history is maintained by bigger ISPs, so smartmessages automatically removes persistently bouncing addresses, unsubscribes, and addresses that have reported your messages as spam. It’s vital these addresses are removed from your lists as ISPs use the bounce rate as a measure of how well behaved you are as a mailer. This is also why it’s a really bad idea to buy big, cheap lists – the high bounce rate will dramatically reduce deliverability to addresses that are good, thus wasting your money.
That it doesn’t come from somewhere known to send bad things	Sources of known bad email are checked using an RBL, a real-time blacklist. This reflects your sending history – you will have to have done something bad to end up in one of these.
That it doesn’t come from somewhere that’s sending too fast	The primary limiting factor in how fast we can deliver your messages is not how fast we can send them – it’s how fast ISPs are willing to accept them. Uncontrolled, full-blast sending is typical of spammers, so ISPs use delivery deferrals (“come back later”) to limit the number of simultaneous connections and/or the message sending rate. Being able to control this carefully and dynamically is one of the things that distinguishes high-end mail servers (like we use) from less powerful ones.
That it comes from someone you know or expect to receive things from	Allowing messages from known senders to pass through filters untouched is referred to as whitelisting. You can ask subscribers to put your address in their address book, and that will usually result in whitelisting of future messages to them. There are commercial whitelisting services, but they can’t guarantee inbox placement and won’t let you get away with bad behaviour.
That it doesn’t contain something you didn’t ask for, don’t want, or might find objectionable	Content/spam filters are extremely fickle beasts and there’s no magic recipe for getting through. Larger ISPs have sophisticated mechanisms for driving their filters from user feedback (clicks on “this is/isn’t spam” buttons) which means the only relevant rule is that spam is whatever an ISP’s users think it is, no matter what you might think! Some ISPs let us know if recipients class messages as spam, and we can use that information to remove those recipients from your lists. Smartmessages provides a SpamAssassin checker for your templates.
That it doesn’t contain something that might damage your computer	This is mostly a special case of the previous check – it’s common to scan incoming messages for viruses, trojans and other malicious software. This is not something we need to worry about as we don’t support the sending of attachments at all.

Uptake and enforcement of these measures varies enormously across ISPs, but they all use a mix of these techniques (and more) in concert to try to ensure their recipients only receive “the good stuff”.

The key to getting your messages delivered is to take all these factors into consideration. The more boxes you can tick, the better your deliverabilty will be – which is what we mean when we say that integrity is the only real defence against spam. If you’re sending spam, you’re part of the problem, not the solution.

All of this means you need to nurture your long-term reputation in every respect – you might get away with sending one spammy message, but next time 99% of your messages may go in the spam folder. The better your sending reputation (i.e. the better your long-term behaviour), the faster and more reliably you’ll be able to deliver in future.