Proposal Exim signature: SMTP error from remote mail server after RCPT TO ... User doesn't exist

[Sebastiano Pilla]

(I’m currently running version 2.4.0 but the pulldown menu has 2.2 as the most recent option).

I’m getting several thousands hits per day to my Exim SMTP servers with random usernames and passwords, this is at least a user enumeration attempt and at worst a brute-force attack.

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The log entries all look like the following:

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2019-07-12 20:51:49 H=([185.222.211.2]) [185.222.211.243]:64692 I=[127.1.0.1]:25 F=[e-mail] rejected RCPT [e-mail]: 127.0.0.1 [127.0.0.1] : SMTP error from remote mail server after RCPT TO:[e-mail]: 550 5.1.1 [e-mail] User doesn't exist: [e-mail]

[Kevin Zheng]

Removing version: 2.2 (automated comment)