你用唔用e-mail 㗎？(nei jung ng jung email gaa?)

你有无邮箱？

Nei yung ng yung email ga ?

Should be ..."Nei yung ng yung email ?"

I would say it depends on the context and intonation. If you pronounce the "呀" a bit longer, it could sound very impatient too. The particle 'gaa3" has several functions and one of them is to form questions. For example "你鍾唔鍾意食朱古力㗎/呀?" (Do you LIKE chocolate?). In this case I would say the particles 㗎 and 呀 both make sense. But it is not always the case. When the 㗎 is used with an action verb (to go, to play, to jog, to use etc) on a question, it means "Do you...(whichever that action is)?" When the 呀 is used with an action verb on a question, it becomes a suggestion. (I am sure there're a few exceptions but I can't come up with any examples right now). Let's see the below example with the action verb "飲" (to drink). e.g. 你 飲唔飲 咖啡呀? (suggestion) It sounds to me that it is asking me if I want a cup of coffee too when my sister is going to get herself one. e.g. 你 飲唔飲 咖啡㗎？ Do you drink coffee? The question here is "Do you use e-mail?", "to use" is an action verb, so I would use "㗎" on my answer below. But if the question was "Do you HAVE (Stative verbs) an e-mail?" I would say the "呀" might sound better than "㗎"，but 㗎 still make perfect sense.