Do the foundry missions that are space and have farm in the title - 1 per day per character should average about 500k if you sell the good stuff on the exchange. Takes 15 mins including the time spent managing the inventory.
Do that hunt thing on Risa at 23 mins past the hour and sell the favors on the exchange, the timer lasts for 15 mins if you have multiple characters do multiple runs.
With those two you'll push 800k+ per day from 20 minutes play, experienced well equipped players would do more faster.
Sell spare duty officers that you get free anyway, gradually you move from white to green, so sell the whites, green to blues sell spare greens etc.
Extreme EC raising - if you have loads of refined dilithium turn it into zen, buy keys 10 pack with the zen and sell keys - 28m EC
What's surprising is no one is mentioning two of the best and easiest EC makers of all ... Selling DoFF's and Contraband on the exchange.
For a KDF / RomKlink toon even a White Prisoner goes for 9-10K EC, and you get plenty of those, and Contraband sells for 40 - 42K each, also easily obtainable.
Although Contraband isn't as easy to come by for Feds, or RomFed's, it can still be obtained, plus Feds get a lot more 'Colonists" and 'Refugee's which can also be sold on the Exchange.
Then of course there is the Green, Blue and Purple DoFF's which depending on there profession and "traits" can be sold for several Million EC.
These can be acquired for free, easily and readily, just by playing the game and running a few DoFF missions ... You don't even have to be logged in for more than a few minutes, to make thousands or even millions of EC.
Make KDF alts
Turn in for dil and convert to zen
Buy more character slots. Make more kdf alts farm more contraband. repeat.
Sell all the contraband for millions daily
mail all the EC/refined dil/Zen to the character of your choice