We're evaluating Xeams for production use as a secure email gateway (firewall mode.)  I'm nearly done with the setup but have run into a problem.  I've sent a test message from my work PC to Xeams and addressed it from my work email address to my personal Gmail address.  The message sits in Xeams outbound queue.  After an hour an NDR is generated.

I'll include all relevant logs below.  I have left MTA-STS enabled.  Our domain is not configured for it.  I also have obtained a LetsEncrypt certificate and enabled the HTTPS, SMTPS ports and enabled STARTTLS.  Xeams ver 9.0 build 6304.

OutboundAuditTrailFailure.log

2024-03-19 17:17:07,947 - [        13] 172.253.123.27,redacted@gmail.com,redacted@redacted.com,748,[Failure reason: MTA-STS is enabled for gmail.com but SSL certificate is not trusted. Error: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target],Test Message

SMTPOutboundConversation.log

2024-03-19 16:46:46,071 - [ 12] ************ New connection to: 142.251.162.26
2024-03-19 16:46:46,086 - [ 12] C --> 220 mx.google.com ESMTP g17-20020a056102081100b00471e6a50a3dsi1306821vsb.580 - gsmtp
2024-03-19 16:46:46,086 - [ 12] S <-- EHLO xeams.redacted.com
2024-03-19 16:46:46,110 - [ 12] C --> 250-mx.google.com at your service, [149.28.109.235]
2024-03-19 16:46:46,110 - [ 12] C --> 250-SIZE 157286400
2024-03-19 16:46:46,110 - [ 12] C --> 250-8BITMIME
2024-03-19 16:46:46,110 - [ 12] C --> 250-STARTTLS
2024-03-19 16:46:46,110 - [ 12] C --> 250-ENHANCEDSTATUSCODES
2024-03-19 16:46:46,110 - [ 12] C --> 250-PIPELINING
2024-03-19 16:46:46,110 - [ 12] C --> 250-CHUNKING
2024-03-19 16:46:46,110 - [ 12] C --> 250 SMTPUTF8
2024-03-19 16:46:46,110 - [ 12] S <-- STARTTLS
2024-03-19 16:46:46,123 - [ 12] C --> 220 2.0.0 Ready to start TLS
2024-03-19 16:46:46,123 - [ 12] ************ New (secure) connection to: 142.251.162.26
2024-03-19 16:46:46,124 - [ 12] S <-- EHLO spam.gohypersonic.com
2024-03-19 16:46:46,172 - [ 12] S <-- QUIT
2024-03-19 16:46:46,172 - [ 12] ~~~~~~~~~~~~ Connection Terminated ( 49)