The letter (or vowel) of "e" consists of three sounds: A) the default one is [ə]; B) when there is an "accent aigu (é)", the sound is [e] (closed e); C) when there is an "accent grave (è)", "accent circonflexe (ê)" or "accent tréma (ë)" , the sound is [ε] (open e). However, when the vowel "e" is followed by two (or three) consonants, such as eSCLavage and eXPRès, that "e" will be pronounced under rule C), i.e., with the sound of [ε] (open e). For such case, it is not necessary to place an "accent grave". Additionally, when "e" is placed at the end of a word, such as "esclavaGE", that "e" will become silent/mute (muet). When "e" is followed by "r" or "z" in verb conjugations, such as "aimER" (1st verb group), and "tenEZ" (present tense of vous-form), that "e" will merge with "r" or "z" to form a combined sound of [e] (closed e). However, if it is NOT the case of verb conjugations, such as "Cher ..." (Dear [addressed to a man/boy in a letter]), that "e" will follow rule C) to become [ε] (open e), and "r" is still pronounced. Here is perhaps considered as an exception. Hence, basically it solves almost all of the problems. For the case of "tenez", the first "e" contains no accent and it is not followed by only one consonant (an "n"), and thus the pronunciation follows rule A), i.e., with the default sound of [ə] ("le" as it was stated in the question). === I wish you a good day.／Je te souhaite une bonne journée.

In my experience, there can be different acceptable pronunciations of the letter e in many cases. If an e is marked with an accent, this is usually how it MUST be pronounced to be considered correct. However, if the e is unmarked, there is a little room for flexibility. Some very common words have unmarked e's, but are pronounced as if they were accented. Consider: descendre is more commonly pronounced as déscendre, depending on the dialect of French. Another example is the various conjugations of espérer. I've heard j'espère pronounced as it's written as well as as if it were written j'éspère. Many of the stem-changing verbs that require either the addition of an accent grave upon conjugation (acheter > j'achète) or will require an accent aigu to be changed to a grave upon conjugation (préférer > je préfère) are subject to this kind of flexibility. All in all, French is not a phonetic language; learning proper pronunciation is a matter of continuous exposure to the language. This will help you learn the little unwritten nuances that most native speakers have. Hope this helps!