This is because it's derived from the English word "email" which is a noun that is traditionally masculine in English.
However, it's important to note that Hindi is a highly flexible language, and the gender of words can sometimes be influenced by context or individual preferences. In some cases, people might use the feminine form of the word "email" (ईमेल) if they are emphasizing the concept of communication, which is often associated with feminine qualities.
But, overall, the masculine form of "email" (ईमेल) is more widely accepted and used in Hindi.