I received and email today from Amazon, lettings me know about several deals. I scrolled through and saw a deal I found potentially interesting. When I clicked on it, I was taken to a general deals page. I thought I'd clicked wrongly and tried again - the result was the same general deals page. So I tried a different deal - same page. This I found frustrating, and I gave up. Not only did I give up, I won't be clicking through from Amazon emails again. So, what have Amazon achieved from sending this email? I would say, into case, it's had a negative impact. I am probably a similar experience away from unsubscribing.
Which brings me to my point. Please think about the content, links and impact of your communications with your customers, especially emails.
This needs to be as relevant as possible for the people receiving it. If you are a retailer that sells in different categories then you could consider a filter on your email subscribe page. This will mean that, for instance, your baby customers won't get emails about your photographic offering. You want your emails to entice customers to click through to your website and browse. That will only happen if there is something in the content that they want to follow up. You can get tech that will report back to you in what was clicked, and where that led. This will give you the data to ensure that you know what content works and what content doesn't.
This leads to impact, where the effectiveness of your content triggers the sales of the product or products you are trying to push. The header of the email is the very first thing seen, so ensure that it leads the recipient to read on. A photo or image makes great headway, especially if the product is visually appealing.
Like the Amazon example above, you need to ensure that the links take your customers to the right places. It means that they have the faith in you and your company to click again and to keep subscribed - this is the lifeblood of your direct email marketing campaigns.
The other consideration is the frequency of your emails - not so often that your customers get sick if you, not so rare that they forget you.
Hope this helps.