Unable to send mail using SMTP on SSL/TLS encryption

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Unable to send mail using SMTP on SSL/TLS encryption

Anvay Singh 41

I'm trying to understand SMTP/POP3 server connection. I have leveraged an Exchange server 2016 as a POP3/SMTP server. I've made all the required changes and have been able to login and send mails using POP3/SMTP from my local machine to exchange server users.

I'm only able to send a mail when I select STARTTLS as encrypted connection type on port 587. If I change it to SSL/TLS. I receive an error:

What changes do I have to make on the server so that I'm able to send mail using SSL/TLS on port 587?

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Answer 1

Aaron Xue-MSFT 2,596 Moderator

Hi @Anvay Singh ,

Secure Sockets Layer (SSL) is being replaced by Transport Layer Security (TLS) as the protocol that's used to encrypt data sent between computer systems.

You could follow below steps to use the Exchange Management Shell to specify the certificate that's used to encrypt authenticated SMTP client connections

1.Run Get-ExchangeCertificate |FL to check which certificate has SMTP service.

2.To specify the certificate that's used for authenticated SMTP client connections, use the following syntax:

$TLSCert = Get-ExchangeCertificate -Thumbprint <ThumbprintValue>  
$TLSCertName = "<I>$($TLSCert.Issuer)<S>$($TLSCert.Subject)"  
Get-ReceiveConnector -Identity "Client Frontend*" | Set-ReceiveConnector -TlsCertificateName $TLSCertName

After the TLS has been set, you could go to owa to verify the correct SMTP settings are displayed.

You also could get more details about the TLS from this document
https://learn.microsoft.com/en-us/exchange/clients/pop3-and-imap4/configure-authenticated-smtp?view=exchserver-2019#step-2-use-the-exchange-management-shell-to-specify-the-certificate-thats-used-to-encrypt-authenticated-smtp-client-connections

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Anvay Singh 41 Reputation points

2022-02-16T04:03:15.953+00:00

I had performed these steps but still I'm able to send test mail only on setting up STARTTLS encryption.

I'm getting the same error when I select 'SSL/TLS' option for 'Use the following type of encrypted connection'

I want to send email on selecting 'SSL/TLS' option under 'Use the following type of encrypted connection'.
Aaron Xue-MSFT 2,596 Reputation points Moderator

2022-02-16T07:38:15.457+00:00

Hi @Anvay Singh ,

The difference between STARTTLS and TLS/SSL protocols is that it is not a protocol at all, but actually, a command issued between an email program and server.

STARTTLS is a Channel Security Upgrade for safer delivery of message.

You could get more details about starttls from this document.
https://mailtrap.io/blog/starttls-ssl-tls/

Please Note: Since the web sites are not hosted by Microsoft, the links may change without notice. Microsoft does not guarantee the accuracy of this information.
Aaron Xue-MSFT 2,596 Reputation points Moderator

2022-02-21T09:17:29.473+00:00

Hi @Anvay Singh ,

It has been a long time since the last reply, did these suggestions help you?

If the above suggestion helps, please click “Accept as answer” to mark helpful reply as an answer. Your action would be helpful to other users who encounter the same issue and read this thread.

Thanks for your understanding.

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Unable to send mail using SMTP on SSL/TLS encryption

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