Envelope
There are three pronunciations (at least) of this word in Received Pronunciation. As a verb, it is realised with the stress on the second syllable 'en-VEL-erp' /In"vEl@p/. (in a minor variation of this, the first vowel can be a clearer _e- sound - like the one in 'hen'/En"vEl@p/. Note that the verb is written ending in _p-: there is no final _e-.
In the noun envelope (which does end in _e-), the stress is on the first syllable. There are two separate ways of realising the first vowel. These can act, for some groups, as in-group markers, and a basis for social exclusivity. I know of no reason why anyone should fall victim to this; but they do. The first pronunciation sounds more |English to my ear - the -e- is realised like the first syllable in the variation recorded above of the verb, like the -e- in 'hen' /"Env@l%@Up/. The other pronunciation of the first syllable is nearer to the French pronunciation /"?Qnv@l@Up/.