ih574

E-MailRelay is what I did and it saved my antique automation capability. Not only did it allow my ISY to send messages successfully, it allows all my ancient cameras and other devices to work again. E-MailRelay is incredibly lightweight, sets up on nearly any PC, and has run reliably for months.
FWIW, I send everything home automation related to a gmail account using an app password. I had given up on messaging from my old SMTP senders (cameras, thermostats, and appliances) long ago when mail relays started requiring TLS and or modern auth. The ISY994 was the last device that could send an email via Google until it also failed. At that time, I troubleshot the ISY-to-gmail.com function and discovered that ISY messages which had a CR/LF in the message body failed. ISY messages with a single line body worked. But any message with a multi-line body failed. I found out that there was some DMARC or DKIM function which failed the message when it encountered a CR/LF. No clue what the details are. That's when I discovered E-MailRelay.