I'm working from memory, but I think you are supposed to do a TLS/SSL negotiation after sending the STARTTLS command. It should not accept any plaintext after the STARTTLS command, so the remote server seems to be working correctly.

Why not use a module like Net::SMTP to do the heavy lifting for you?

Hi:

I have already looked at that and several others

I my have to do that as a fallback, but that ruins my "learning experience". Or perhaps that would be a better learning experience.

Thanks for suggestion

When I go through the steps using openssl, after the STARTTLS and the go ahead I send EHLO and the server sends back expected responses the I send the AUTH PLAIN and it is accepted. Perhaps openssl is doing something with negotiations in background of which I am unaware

RFC 3207 shows a typical exchange:

   S: 250-STARTTLS
   S: 250 DSN
   C: STARTTLS
   S: 220 Go ahead
   C: <starts TLS negotiation>
   C & S: <negotiate a TLS session>
   C & S: <check result of negotiation>
   C: EHLO mail.example.com
   S: 250-mail.imc.org touches your hand gently for a moment
[download]

I don't know specifically what these three example communications are: C: <starts TLS negotiation> C & S: <negotiate a TLS session> C & S: <check result of negotiation>.

Using openssl I go from S: 220 Go ahead to EHLO and it works up to the pint of a cert failure when I send the RCPT TO:

Hi tultalk:

I don't know specifically what these three example communications are: C: <starts TLS negotiation> C & S: <negotiate a TLS session> C & S: <check result of negotiation>

This part would do a public key exchange and negotiate a private key for this session. After this step all data going to the server must be encrypted by openssl before sending, and all data coming from the server must be decrypted by openssl before it is usable

The IO::Socket::SSL has an example of how to upgrade a socket from plain to SSL, assuming you are using IO::Socket::INET as the base socket. Search for "Talk Plain and SSL With The Same Socket" in the docs. I haven't looked at the code it uses, but I'm assuming that it re-blesses the socket into IO::Socket::SSL, and after that the IO::Socket::SSL module will encrypt any data you write to the socket before sending to the socket, and decrypt any data it reads from the socket before giving it to you.

In the example above I didn't see any SSL modules, so I assumed you were still writing plaintext directly to the socket. If that's not the case, could you show the part that does the ssl negotiation and adds the layer to encrypt/decrypt?

If you want a learning experience, Net::SSLeay directly exposes the openssl library's low-level functions to negotiate sessions, and encrypt/decrypt data. I've never used it directly myself, but I would imagine that there are some good examples in the IO::Socket::SSL sources.

Works using openSSL cmd

250 HELP
ehlo
250-cp15m2.lowesthosting.com Hello  [72.168.128.19]
250-SIZE 52428800
250-8BITMIME
250-PIPELINING
250-AUTH PLAIN LOGIN
250 HELP
AUTH PLAIN d2VibWFzdGxxxxxxxxbS51cwB3ZWJtYXN0ZXJAYndtamNtLnVzAHdtQDQwO
+TEzV00=
235 Authentication succeeded
[download]

First of all, you might want to completely edit out what looks right now like slightly damaged but partially decodable login-password pair, in case you didn't do that already.

Secondly, when you're using openssl, you are already establishing a TLS connection (so no STARTTLS command is required), but when doing STARTTLS in Perl by hand (like you seem to be trying to), after receiving 220 TLS go ahead you should immediately send TLS Client hello, establish a TLS connection and send EHLO abc.us over that. Judging by your code,

        socket_write("STARTTLS$CRLF")
             || return fail("send STARTTLS failed (lost connection?)")
+;
        socket_read()
             || return fail(" $server_reply");
        socket_write("EHLO $smtp$CRLF")        
             || return fail("send EHLO error (lost connection?)");
[download]

you are trying to authenticate in plain text, not over TLS (thus defeating the purpose of the command). Since server expects TLS handshake and not a EHLO, it bails.

Suggested solution: start right away with TLS. This way, you won't have to create a TLS object over an existing TCP connection, thus slightly breaking encapsulation in your application architecture, and bad guys sitting between you and the server and doing a MITM attack won't be able to impersonate the server at all (like they can before you enter STARTTLS).

Thanks

chunks removed and some replaced with xxxxx