Sendmail: did not issue MAIL/EXPN/VRFY/ETRN ...
error:
sm-mta[46435]: wAILdB5W046435: [185.228.80.55] did not issue MAIL/EXPN/VRFY/ETRN during connection to MTA
what is happening ?
SMTP expects commands in the following sequence:
HELO or EHLO servername MAIL FROM: <address> RCPT TO: <address> DATA
Though technically instead of MAIL FROM, the server could send EXPN, VRFY, or ETRN, though nobody ever does.
Apparently your server got the HELO or EHLO greeting, but then nothing after that, or something after that wasn’t expected.
Often this comes from monitoring agents or other scanners who aren’t interested in actually sending mail, but rather just testing to see what’s listening. Also, it’s quite likely that they’re attempting to exploit some old vulnerability, which is (correctly) simply being interpreted as garbage and terminating the connection.
Typically when a server takes some unusual steps (such at prematurely terminating a conversation) it will make a log entry noting the fact, just in case you need to debug it later.
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