The words males, mails sound the same but have different meanings and spellings. Why do males, mails sound the same even though they are completely different words?
The answer is simple: males, mails are homophones of the English language.
Third-person singular simple present indicative form of mail.
Plural form of mail.
The mail delivery system.
Plural form of male.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.