These are logins and passwords of last 50k login attempts into my server.
All of them failed, because there is no imap/pop/smtp login option on this server at all.
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Column "host" shows which of my servers the email arrived at,
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"port" - what port they connected to (25, 143, 465, 587, 993),
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"proto" - what protocol were they talking (smtp, imap, pop3, defined by port).
Note that hostname of this host is hidden from the logs in order to avoid spam.