External email delivery failed after renewing exchange self signed certificate


Recently our exchange server 2016 self signed certificate about expired on November. We renew the certificate on November before it expired and everything was good until last couple day. Out of the blue one of the external party not able to send us email and getting bound back referring our certificate expired. 

"'450 4.4.317 Cannot connect to remote server [Message=CertificateExpired] "


12/1/2022 3:16:02 AM - Server at FQDN returned '550 5.4.317 Message expired, cannot connect to remote server(CertificateExpired)'
12/1/2022 3:14:50 AM - Server at ABC.COM (1XX.XX.XXX.XX) returned '450 4.4.317 Cannot connect to remote server [Message=CertificateExpired] [] [LastAttemptedIP=1XX.XXX.XXX.XXX:25] [SmtpSecurity=-1;-1] [FQDN](CertificateExpired)'


Other external domain was able to send and received just fine, only happen to this specific domain. 


1 Reply
best response confirmed by Don_Vlogeer (Contributor)
after checking couple of thing, realize it was the mail security gateway certificated expired. upon renewing the cert, all went well