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Test IMAP connection to Outlook using OpenSSL – PHP Versions

I am trying to access the Outlook mail server via IMAP using PHP. As this is not working as intended and the error messages are not helping, I looked up ways to test the basic connectivity and came across the following line of code:

openssl s_client -connect outlook.office365.com:993

This should, supposedly, let me connect to the mail server using an encrypted connection, so that I can then issue some commands to actually log in etc.

However, the command only generates the following output:

CONNECTED(00000003)
write:errno=104
---
no peer certificate available
---
No client certificate CA names sent
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SSL handshake has read 0 bytes and written 313 bytes
Verification: OK
---
New, (NONE), Cipher is (NONE)
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
Early data was not sent
Verify return code: 0 (ok)
---

I have tried researching the error message (write:errno=104), which lead to some suggestions like enforcing TLSv1.2 using the -tls1_2 parameter, neither of which made any difference.

Can someone point me in the right direction? I already ran this command on Ubuntu and Windows 10 using the latest version of OpenSSL.

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2

Answers


  1. 0

    I can connect using your command, but I needed to force rn line ending characters using the -crlf option when connecting in order to be able to type commands and have the server recognise them.

    You can also add -quiet to reduce the amount of output:

    openssl s_client -connect outlook.office365.com:993 -crlf -quiet

    However, it seems the connection is getting reset in your case. This means there’s some sort of network issue. There might be a firewall blocking your access to port 993 on outlook.office365.com. e.g. this might be the case if you normally have to connect via a proxy server.

    Recent versions of openssl s_client have a -proxy option, but don’t seem to allow specifying a proxy username and password. Also it might not work with your proxy even if you don’t need to authenticate to the proxy server. One workaround might be to use http://ntlmaps.sourceforge.net/. I have tried it in the past, but it was over 15 years ago.

    You could also try using cURL‘s IMAP support instead of openssl s_client, since it has better proxy support.

    Another possibility is to connect to port 143 and use STARTTLS instead of connecting to port 993. Obviously if port 993 is firewalled then port 143 might also be, but in your case it seems like it is allowed:

    openssl s_client -connect outlook.office365.com:143 -starttls imap -crlf -quiet
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  2. 0

    If you are behind a proxy and can’t connect to the IMAP server directly, then you can also use something like EmailEngine that handles connections itself and allows access mailbox contents via a REST API.

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