2700110 - Error code XS751 with STARTTLS occurs in tranasaction SOST during mail sending

Error message XS751 "Message cannot currently be transferred to node & due to connection error" occurs in transaction SOST when a mail cannot be sent from SAP system. The long text contains the "451 TLS required but server does not offer STARTTLS" error message and you can find the HELO keyword instead of EHLO in the level 3 ICM trace which means the standard SMTP protocol is used for the communication.

SAP Basis 731 006 or higher with Kernel 721 or higher.

XS751, XS 751, STARTTLS, "Message cannot currently be transferred to node & due to connection error", SOST, SMPT, TLS, TLS authentication, server does not offer STARTTLS, 451 TLS required, "Nachricht an Knoten & wg. Verbindungsfehler momentan nicht übergebbar", mail sending error, email, email sending , KBA , is required to send mail , 5.7.3 starttls is required , BC-SRV-COM , Communication Services: Mail, Fax, SMS, Telephony , Problem