Outgoing email encryption not working (SMTP)

I need a solution


I have a problem with sending out encrypted emails using Outlook 2016 and Symantec Encryption Desktop. The odd thing is that I can receive and decrypt emails without any issues, but outgoing emails are blocked.

Outlook is configured to use ports 25 for SMTP and 143 for IMAP. Ougoing server requires authentication and uses the same settings as incoming server.

Symantec Encryption Desktop is configured with email proxy enabled and ports 465 for SMTP and 993 for IMAP, as mail server requires SSL/TLS. 

Outlook error message states that the connection was interupted without any further details. Verbose Symantec logs show:

Email Verbose Connection accepted

Email Verbose Found exisiting account list entry for [IP]

Email Verbose Existing entry is [email address]

Email Verbose Proxying SMTP

Email Verbose Attempting to connect to server at [IP]

Email Verbose Attempteing tunneled TLS connection on port 465

Email Verbose Successfull connect on port 465

Email VerboseTLS session established with [mailserver]

Email  Error Cannot connect server socket to [IP]

Email Warning Tunneled TLS negotiation with server failed.

When I change the port 25 to 465 in Outlook I can send out emails fine, but I loose the ability to encrypt them.

As this is a test machine – there is no AV software onboard which could be blocking it. Windows Defender and Firewall are disabled completely.

Any ideas what might be causing this error?

Software versions:

OS is Windows 10 Pro N,

Symantec Encryption Desktop 10.4.1 

Tahnk you,



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