Why am I receiving spam emails at unique internal testing email addresses?

Email marketer from StackExchange responds that it is possible spammers will attempt to generate email addresses by simply trying every combination of letters until one works.

Email marketer from Reddit responds that their email address, used solely for a specific website, started receiving spam after the website suffered a data breach, even with a unique address.

Email marketer from Neil Patel shares that spammers obtain email addresses through various methods, including purchasing them from data brokers, scraping websites, and using email appending techniques. He also mentions that data breaches are a common source.

Email marketer from Email Geeks shares that they receive small amounts of strange spam on Gmail accounts used only for testing/dev work, suggesting data leakage or random probability as potential causes.

Email marketer from Bounteous responds that even unique or obscure email addresses can end up on spam lists due to data breaches, email harvesting bots, or being included in purchased lists by unscrupulous marketers.

Email marketer from Quora responds that data breaches are almost certainly the reason you are getting spam to a very unique email address.

Email marketer from Search Engine Land explains that spammers often use dictionary attacks, combining common names and words to guess email addresses, and data breaches can expose email addresses even if they're not publicly listed.

Email marketer from Website Advisor responds that, "Email addresses are harvested from websites, chat groups, and customer lists. They are also created by 'dictionary attacks', in which programs generate every possible combination of letters and numbers."

Expert from Email Geeks believes any email address in a Windows account is potentially compromised, regardless of precautions.

Expert from Email Geeks notes that while unsubcentral data leaks are possible, it's hard to confirm with just a single instance.

Expert from Word to the Wise shares the strategy of using plus addressing (e.g., myemail+website@example.com) so you know who shared your email address if you start getting spam.

Expert from Email Geeks suggests that a Windows desktop compromise could leak the email address to spammers, even if it doesn't indicate a server breach.

Expert from Email Geeks says that the likelihood of random email generation depends on the entropy of the email address.

Expert from Spam Resource explains that spammers sometimes guess at email addresses, though it's generally inefficient. If your address is short or contains common words, it's more likely to be guessed.

Documentation from FTC explains that spammers often collect email addresses from the internet, including from website contact forms and email lists. They also note that some companies may sell or share email addresses with spammers.

Documentation from Spamhaus explains that spammers use sophisticated techniques like address harvesting from websites, buying lists of email addresses, and using dictionary attacks to generate possible email addresses. They also mention that data breaches are a significant source of harvested email addresses.

Documentation from Microsoft details that spammers obtain email addresses through various means, including scraping websites, purchasing lists, and guessing addresses. They also note that if you've used your email address to sign up for a service that was later compromised, it could be the source.