By Rodney Amato

Email deliverability can be tricky. You have to deal with spam filters, blacklisting, whitelisting, bounces and more. In this article I'll share with you 20+ tips to make sure your emails get delivered. If you're looking for a complete email marketing solution which includes the software to create campaigns, the server and MTA to send email, and expert email deliverability advice, you may be interested in our enterprise email marketing product, ViaNewsletter.

Frequency and subscription

• Never send an email to someone that won't be expecting to get an email from you. Make sure all your sign ups are clear and are double opt in
• Make sure you regularly (7 or 8 days after every send to allow for delivery attempts to non existent domains) remove emails from your list that are bouncing or you may end up sending to spam traps
• Send a smaller email weekly rather than a large one monthly. This will allow you to keep your list more up to date and will keep your newsletters as something expected to your users and less likely to be marked as spam. Smaller emails are also easier for your customers to skim amongst their other emails.
• Always include an unsubscribe link in your emails
• Test and make sure the unsubscribe link actually works. If the unsubscribe returns an error they may just mark you as junk instead of letting you know it's broken
• Never try to hide who the email is coming from
• Make sure who the email is coming from is going to be who the subscribers expects it to be coming from
• Make the unsubscribe process easier than the subscribe process

Server Setup

• Ensure your mail server is not an open relay - Wikipedia has some information on what this means.
• Ensure that postmaster@yourdomain.com and abuse@yourdomain.com go to someone that can and will actually do something about complaints
• Make sure your forward and reverse dns for your mail server match up
• Ensure your email server is not listed on any RBL (realtime black lists)
• Setup SPF for you domain so that other people have a harder time pretending to be you. This can also help with Hotmail deliverability (SenderID actually but in most cases it works out to the same thing)
• Setup domainkeys to help with deliverability to Yahoo mail accounts
• Some web mail systems (e.g. Hotmail) base (at least in part) junk filtering on the reputation of your ip address. If you have only just gotten an IP and are getting filtered to the junk then you may need to build up reputation as a legitimate mailer before you stop getting filtered to the junk mail folder
• DKIM will become more important in the future but for now (July 2007) it doesn't seem to be used by anyone
• Ensure that you send from a domain which actually has MX records setup in DNS and that each mail server listed will accept mail for the domain you are sending from

Email content and design

• A pretty email is nice to look at but the most important thing is getting your information to your subscriber so don't get too fancy with the design. Lots of design elements will get stripped out by mail clients and Outlook 2007 will display hardly any of them
• Don't use spam like words and phrases in your email
• If you include a text part (and you should) be sure to have the content of that be a true text representation of the text in the html version
• Don't include too many images in your email (1-2 per email should suffice) or some filters will flag it
• Don't use a similar colour for your text as the background it is on (e.g. medium gray text on light gray background) or some filters will see that as trying to hide text
• Don't use images or send attachments that are too large. 300Kb should be the absolute max size of the email so be sure to make sure the total for images and attachments comes in well under that (adding a file to an email will increase the size by about 30% just in encoding it) so you need to take that into consideration too
• Make sure the content of the email is what the subscriber signed up to receive. Don't send them emails about sprockets if they only wanted to know about cogs.
• Don't include a single large image in your email if you can avoid it since this is how most spam nowadays seems to operate