1. Blatant Lack of Permission
Companies still try to get around the permission issues in search for the quick buck. That’s a big mistake.  

2. Utterly Deficient Segmentation 
Content relevancy is the number one issue for the email marketer. Without segmentation, you have no real relevancy.

3. Lame ‘Welcome’ Messages
We still receive far too many lame welcome messages. What a wasted marketing opportunity.

4. Frequency Decisions Made for the Wrong Reason 
Marketers are in a constant battle on the matter of frequency.

5. Institution-to-One Messaging 
The debate on how to personalize company emails is ongoing. It’s all about testing.

6. No Real Interactivity 
Interactivity is not only for social media. Email was once the relationship building medium, and it still can be.

7. Deliverability: Content, Formatting & Lack of Self-Advocacy 
If anything, deliverability is even a bigger issue than it was two years ago.

8. Designing Images That Appear as Red Xs 
Getting HTML images to appear for those who have images turned off still requires that they turn the images on. It’s the text vs. HTML debate.

9. Disregarding Your BlackBerry and Mobile Readers 
The number of mobile readers has exploded since 2008. Thank you Iphone and Android. It’s more important than ever to make your email mobile reader friendly.

10. Repeating Ad Types 
Banner blindness in email newsletters is more prevalent than ever. 

11. Collecting Bad Response Rates
You need good analysis to determine the effectiveness of your email. That’s always been the case. 

12. Relying on Email Only 
This last mistake of relying on email only was written during the dawn of the social media revolution. It’s the only one that feels a bit dated, but it’s still worth noting that relying on just one tactic alone is never a good plan. 

Source: MarketingSherpa report "Dirty Dozen: Email Newsletter Mistakes Nearly Everyone Makes"