I know I can use “Communicate” to send email to a specific “Mailing List” but need to find way to prevent duplicates, even manually if need be.
What I meant was sending mail to a whole user groups (all “Members”, say) as opposed to a mailing list. “Send to Member Groups” instead of “Send to Mailing Lists”, so to speak.
Is there a way to export from Mailing List to sort, for example, in excel for duplicates. I can always go back into Mailing List and delete the duplicates manually.
Yes, of course. This article should get you started; once you have a list of mailing addresses, you just need to find the duplicates.
Or is ExpressionEngine simply not the ideal program to send out enewsletters
It’s certainly not its main purpose, no. It serves basic needs well, I found, but if you require more sophistication a different, specialized solution might be worth considering.