... My e-mail client on my 12-year-old Vista Home Premium SP2 32-bit laptop is, to this day, the default one provided by the OS, i.e. Windows Mail; while I rarely use today IE9 itself to browse the web, Windows Mail does use the IE9 engine to preview and display e-mails; without TLS 1.2 support present (in IE9), you risk having e-mails, certainly the ones in Rich Text (HTML) format, render broken, e.g. if in-line images are served exclusively over TLS 1.2!
Using Windows Mail in 2019 might not be the smartest choice security-wise; but AFAIAA, very few current e-mail clients are being actively developed with Vista in mind; the one several of our XP friends have migrated to is the Interlink (a Win7+ client developed by notorious Matt A. Tobin) fork called MailNews, maintained by roytam1, the same dev who gives us New Moon 28 and Serpent 52.9.0/55.0.0!