The received letter, most likely, is the result of so called "dictionary attack". Spammers often use the software for casual guessing of email addresses by words from the dictionary.
Spammers use such lists of addresses for mass mailings. If you don't see your address in fields "To" or "Copy", it means that you have received the hidden copy of spam (your address has been entered in the field "Blind carbon copy"). There are cases when you also can see your address even in the field "From" (i.e. you receive letters from yourself).
Never respond to spam emails or follow the hyperlinks provided. This will only confirm that an email address is valid and lead to more spam.
See here for more details about spam.
Some advices of how to reduce spam amount in the mailbox.
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