It's pretty amazing how many pitfalls and gotchas there are when dealing with email deliverability. I'm going to spend some time explaining the path that email can take from your server to a customer's inbox. I'll also go over the protocols and services you can use that help improve your sender score, resulting in better email deliverability.
If you have a new IP address (such as if this is a new domain, or you've moved to a new server), or if you're using an IP address that has a bad history (could often happen with shared hosting), it's likely that your email will end up in a Spam folder. This is because your IP has no (or a bad) reputation.
This is also known as "warming up" your IP. If possible, every day, you should send out more and more emails, slowly inreasing the volume. A general rule of thumb is to start with 2-3k emails per day and increase by a thousand per day.
After mailing consistently for 30 days from your new IP, your reputation score should increase.
There's many factors at play when your reputation score is calculated:
I'll go over them in detail below.
If you authenticate your outgoing emails with SPF and DKIM, this greatly increases your sender score, and reduces the chances your email will be flagged as Spam.
Similar to SPF and DKIM, by setting up a reverse DNS record, you improve your email deliverability.
When subscribers mark your email as Spam, this obviously isn't a good thing, but specifically it can reduce your sender score by 40 points, if you reach 1.5%+ spam complaints.
A feedback loop is a system that allows email provides to notify domain owners when their emails are being marked as spam. That way you can unsubscribe the users from your list and stop emailing to them, thus reducing the repeated spam complaints.
Lucky for you, Winning Email offers a service that will setup feedback loops for you at 10+ of the popular email providers:
This may be an obvious one, but always make sure the subscribers you're mailing to have given you permission to email them. Using a double opt-in process (the subscriber has to verify their email address before they're active on your list) is a smart plan. You should also make sure you only email your subscribers relevent content, and don't spam them with stuff they're not expecting.
The ideal complaint rate (a complaint happens when someone clicks the Spam button in their email client) is 0.1% (that's 1 Spam complaint per 1000 emails). Do your best to only mail relevant content to your subscribers in order to keep your complaints low.
When you try to send to an address that doesn't exist, the target mail server will bounce your email with an error of something like "unknown user". If these bounces get up to 10% of your campaign, you could become blocked from emailing to that domain. So make sure your users have double-opt-in'd to your list.
Also, once you receive these bounces, you should remove these non-existent addresses from your list, so you don't mail to them again. You also don't want to buy a list from a 3rd party, as they're usually "dirty" and contain a lot of unknown users.
The ideal rate of unknown users is 2% or below.
A Spam Trap is a decoy email account used to catch spammers. High quality senders typically never send to spam traps. If you do send to one, your sender score could be penalized by as much as 40 points.
It's good practice to monitor your sender score before and after every send. You can do that by using senderscore.org.
A score of 90 is a good target to shoot for. Good luck!
Kane Miller from Winning.Email
Kane has a background in computer engineering, but now focuses on creating new and interesting web services. His passion for improving his own email deliverability rates was the driving force behind the creation of Winning.Email.