That's quite a judgmental generalization, Zawerg. Duden indicates that [ˈkafeː] is the standard pronunciation, while [kaˈfeː] is an Austria variant. See also: http://www.atlas-alltagssprache.de/runde-4/f23a-c/ http://prowiki.ids-mannheim.de/bin/view/AADG/KaffeeAkzent
Listen to it here: https://forvo.com/word/und/#de
Basically it's supposed to be like unt.
In fluent natural speech, it can sometimes sound like un -- a bit like how English and in fluent natural speech sometimes turns into 'n' as in this 'n' that. But that's not the "default" pronunciation.
Best to start with the "proper" pronunciation and let colloquial slurrings and contractions come naturally later after you've heard and spoken a lot of German.
Neither of these words are feminine, though, nor do they end in -ei. Nor do most feminine words end in -ei in German. There are a number of endings or even none at all.
That's a lot different from Spanish.
It really does seem like less effort to just remember each individual word's gender than to memorise the complicated list of endings for each gender (and then still have to remember the ones that don't have any specific ending).