Sendmail sends test emails after installation. How to stop it?

Question

send mail

I installed sendmail, tested it like this (taken from the Internet):

spoiler

# telnet localhost smtp
нам выдает:
Trying ::1...
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 localhost6.localdomain6 ESMTP Sendmail
8.14.3/8.14.3/Debian-9.2ubuntu1; Thu, 9 Dec 2010 15:31:17 +0200;
(No UCE/UBE) logging access from: localhost.localdomain(OK)-
localhost.localdomain [127.0.0.1]
вводим:
HELO localhost
нам выдает:
250 localhost6.localdomain6 Hello localhost.localdomain [127.0.0.1],
pleased to meet you
вводим:
MAIL FROM: [email protected]
нам выдает:
250 2.1.0 [email protected] Sender ok
вводим:
RCPT TO: [email protected]
нам выдает:
250 2.1.5 [email protected] Recipient ok
вводим:
DATA
нам выдает:
354 Enter mail, end with "." on a line by itself
вводим
test message
.

Tested yesterday at 23 o'clock, now test letters periodically fall. How to stop it?