The Spanish vowel e has a sound that can vary depending on its location in a word. Its pronunciation also varies somewhat among various regions and even with individual speakers.
The most common sound for e is much like the English "e" sound in word such as "test" and "wrench." This sound is especially common when the e is located between two consonants.
Sometimes, the e is similar to the vowel sound in English words such as "say" - but shorter. Some explanation is in order here. If you listen carefully, you may notice that for many English speakers the vowel sound in "say" is made up of two sounds - there's an "eh" sound that glides into an "ee" sound, so the word is pronounced something like "seh-ee." When pronouncing the Spanish e, only the "eh" sound is used - there's no glide into an "ee" sound. (In fact, if you pronounce the glide, it becomes the Spanish diphthong ei rather than e. As one native speaker using the nickname Didi explained recently in our forum: "As a native I'd say that the most accurate pronunciation for that e sound is like that in 'bet' or 'met.' The sound of 'ace' has an extra vowel sound that makes it unsuitable."
The variable nature of the e sound also was explained well in this forum post by Mim100: The simple vowel e can be rendered anywhere across a range of tongue heights, from roughly mid-low (or mid-open), resembling what you hear as 'por-KEH,' to mid-high (or mid-closed), resembling what you hear as 'por-KAY.' The key feature of the simple vowel e is that it is pronounced somewhere within that range of tongue height and that the tongue does not change height or shape during the course of pronouncing the vowel. Standard Spanish does not distinguish between words based on how open or closed the vowel e happens to be pronounced. You may hear a more open pronunciation more often in closed syllables (syllables that end in a consonant), and you may hear a more closed pronunciation more often in open syllables (syllables that end in a vowel)."
All this may make the pronunciation sound a bit more difficult than it is. Pay attention to how you hear native speakers pronounce the vowel and you'll soon have it mastered. Phrases pronounced by native speakers in our audio lesson on pronouncing the e are "¿Cómo está usted?" "Muy bien, gracias, ¿y usted?" "Buenos días, señor" and "Hola, ¿qué tal?"