No, I'm not getting an error response from my outbound SMTP service. My service IS my outbound SMTP server. I'm using the Rebex libraries to connect directly to the SMTP servers of the receipients. The error I get is during my connection to the SMTP server that is requiring TLS.
2018-02-06 16:31:51.316 INFO : Response: 454 4.7.0 Connection is not TLS encrypted. Recipient organization requires TLS. [BN3NAM04FT046.eop-NAM04.prod.protection.outlook.com]
2018-02-06 16:31:51.316 INFO : Command: RSET
2018-02-06 16:31:51.348 INFO : Response: 250 2.0.0 Resetting
2018-02-06 16:31:51.348 ERROR : Info: Rebex.Net.SmtpException: One or more recipients rejected. Call SmtpException.GetRejectedRecipients() to get a collection of rejected email addresses.
at Rebex.Net.Smtp.QAP(Boolean C, String R, EFO O, String I, Int64 D)
at Rebex.Net.Smtp.HAP(String C, String R, String O, Stream I, TransferEncoding D)
at Rebex.Net.Smtp.XJP(MimeMessage C, Stream R, MailAddress O, MailAddressCollection I)
at Rebex.Net.Smtp.IJP(MailMessage C, MailAddress R, MailAddressCollection O)
So what you refer to configuring my outbound SMTP server to use TLS when possible, is exactly what I'm asking. How should I be configuring and performing the SMTP Connect in order to support TLS.