I don't know too much about Russian, but I strongly suspect that even if Russians can understand a foreigner who fails to make the distinction, the foreigner will have lots of difficulty understanding when native speakers talk. I would guess that a relatively small investment in time getting the sounds right in the first place (before you've memorized 10000 words with the wrong pronunciation) will pay huge dividends as one learns the language.

I guess it is Далена, "э" is only used in "это", in diphthongs ("аэро..." for example) and in loanwords.

Спасибо далэна! (I tried to spell your name in Russian, it's probably wrong) 

I think I'll just try and pick up the pronunciation as I go.

Wow, I was watching a Youtube video and the guy was making a pretty big deal over them. That's good to know, and thanks for your reply!

Большое спасибо!

This article can help you:

http://www.babylon-project.com/learn_russian/russian-alphabet/