Hope you're doing great! Let's take 1999 as the year of email marketing's birth. 13 years old advertising niche. But how email marketing changed since 1999? I will not talk about huge amount of email advertising agencies, services and all the global things and progress - let's stick to the basics of email marketing.
1. Just email. back in 1999 it was just email-only marketing - 1 sender, few recipients, direct advertising with an offline info. Nowadays we mix it a lot - we include social media and social network accounts in our mailings, we allow social network fans to become our email subscribers and we allow email subscribers to become our fans. We provide our subscribers with the information type they want. Email marketing is mixed with all the other types of online marketing these days.
2. Email lists. Email list building really changed! On the one hand there weren't so much email addresses back in '99, on the other hand - we had no CAN SPAM Act. Marketers gathered and crawled email addresses any way they could. This was a time when quantity was over quality.
3. Subject lines. Back in 1999 email marketers used just few-word subject lines, which looked short and sweet. Sure, there were no personalization at all. Nowadays we use subject lines that are personalized, informative and include call-2-action. Also spam-filters were different back in those days - for example word FREE was a high-risk spam alert for most email service providers and filters. Nowadays spam algorithms are smarter and more sophisticated.
4. Statistics. Some say that email marketers tracked open rates, click-through rates and conversions only back in 1999. I don't believe in that, no data were tracked at all, I guess, except approximate sales. Nowadays we use modern tracking services and software that allows us to track Average Order Value, Sales per Email Address, Reach, and many other activities.
As you can see email marketing is not an advertising "shotgun" anymore, like it was back in 1999 - it's a smart, highly targeted and personalized laser-canon.