Nodemailer: Process-global DNS cache reuses TLS `servername` across transports, enabling cross-tenant SMTP credential disclosure

Summary Nodemailer's process-global DNS cache is keyed only by host, but each cache entry also stores the caller-specific TLS servername. When two direct SMTPS transports use the same DNS host with different tls.servername values, the first transport's server name is returned to the second...