what has he got the sockets connection type set to ?
https://documentation.xojo.com/api/networking/sslsocket.html#sslsocket-sslconnectiontypes
SSLv23 gives bets compatibility
and auto fall back
the others do not automatically revert to something lower & less secure
the other thing to check is what smtpconnectiontypes is set to
https://documentation.xojo.com/api/networking/smtpsecuresocket.html#smtpsecuresocket-smtpconnectiontypes