telnet smtp.server.com 25
Trying 192.168.1.10...
Connected to smtp.server.com.
Escape character is '^]'.
220 oracle 04
EHLO
250-NG-server.com Hello [10.89.74.69]
250-SIZE 25165824
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-STARTTLS
250-8BITMIME
250-BINARYMIME
250 CHUNKING

declare
  l_connection utl_smtp.connection;
  crlf varchar2(2) := UTL_TCP.CRLF;
  l_mailhost VARCHAR2 (64) := 'smtp.server.com';
  l_from     VARCHAR2 (64) := 'no-reply.abc@server.com';
  l_to       VARCHAR2 (64) := 'no-reply.abc@server.com';
  l_subject     VARCHAR2 (64) := 'oracle';
  
begin
  l_connection := utl_smtp.open_connection(
    host => 'smtp.server.com',
    port => 25,
    wallet_path => 'file:/u01/wallet/my_wallet',
    wallet_password => 'password',
    secure_connection_before_smtp => false);
  
  utl_smtp.ehlo(l_connection, 'smtp.server.com');
   utl_smtp.starttls(l_connection);
  utl_smtp.auth(l_connection, 'login', 'password',utl_smtp.ALL_SCHEMES);

utl_smtp.open_data(l_connection);

UTL_SMTP.write_data (l_connection, 'Date: ' || TO_CHAR (SYSDATE, 'DD-MON-YYYY HH24:MI:SS') || crlf);
  UTL_SMTP.write_data (l_connection, 'From: ' || l_from || crlf);
  UTL_SMTP.write_data (l_connection, 'Subject: ' || l_subject || crlf);
  UTL_SMTP.write_data (l_connection, 'To: ' || l_to || crlf);
  UTL_SMTP.write_data (l_connection, '' || crlf);

  FOR i IN 1 .. 10
  LOOP
    UTL_SMTP.write_data (l_connection, 'This is a test message. Line ' || TO_CHAR (i) || crlf);
  END LOOP;
  
UTL_SMTP.close_data (l_connection);
UTL_SMTP.quit (l_connection); 
end;

openssl s_client -connect xx.xx.xx.xx:25 -starttls smtp


CONNECTED(00000003)
depth=0 C = RU, ST = Moscow, L = Moscow, O = something, OU = IT, CN = ng-smtp-01.com
verify error:num=20:unable to get local issuer certificate
verify return:1
depth=0 C = RU, ST = Moscow, L = Moscow, O = something, OU = IT, CN = ng-smtp-01.com
verify error:num=27:certificate not trusted
verify return:1
depth=0 C = RU, ST = Moscow, L = Moscow, O = something, OU = IT, CN = ng-smtp-01.com
verify error:num=21:unable to verify the first certificate
verify return:1

No client certificate CA names sent
Server Temp Key: ECDH, prime256v1, 256 bits

SSL handshake has read 2689 bytes and written 466 bytes

New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES256-SHA384
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
Protocol  : TLSv1.2

Verify return code: 21 (unable to verify the first certificate)

250 CHUNKING

No client certificate CA names sent
Server Temp Key: ECDH, prime256v1, 256 bits
---
SSL handshake has read 2689 bytes and written 466 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES256-SHA384
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES256-SHA384
    Session-ID: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    Session-ID-ctx:
    Master-Key: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    Key-Arg   : None
    Krb5 Principal: None
    PSK identity: None
    PSK identity hint: None
    Start Time: 1589910807
    Timeout   : 300 (sec)
    Verify return code: 0 (ok)
---
250 CHUNKING
451 4.7.0 Timeout waiting for client input
read:errno=0