1. Unsolicited messages (but you don’t believe they are)
Are you absolutely sure that you have your customers’ consent to send them a specific message? If you send a commercial message to customers (or prospects) who did not subscribe to receive such messages from you in a direct and verifiable way (i.e. they received a subscription confirmation request and confirmed the subscription), you are sending SPAM. It doesn’t matter if you believe it isn’t, or if you think that the recipients will definitely be interested in what you are about to tell them. Don’t do it. It will negatively impact your reputation, the perception and respectability of your brand, the deliverability of future messages (as users will complain), and – of course – the effectiveness of the message itself.

Some businesses send spam because they believe it has a positive return on the investment. Apart from being illegal, unsolicited messages typically have a minuscule return on the investment. Responsible and well-managed marketing campaigns – even on small numbers – will deliver a much higher return.

2. Sending without testing
It’s a jungle of desktop- and Web-based email software out there! That said, many businesses can spot and resolve problems in just a few minutes by testing a message on the most popular email clients (e.g. Hotmail, Gmail, Yahoo!, Outlook,…). Make sure links work, images are loaded correctly (once permission has been granted), and there are no grammar and spelling mistakes. Then, focus on how the message is displayed across the different email programs.

For a more in-depth review of the message, you can use a service like Email Analysis.

In terms of testing the results of a campaign – if you are becoming a pro – you can use A/B testing to test variations of the same message on a small portion of the list, and then send the best-performing one.

3. Underestimating subject and sender
Read more