Unable to send mail using SMTP on SSL/TLS encryption

Question

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?

Answer 1

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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