I use yahoo instead of gmail but understand the frustration. I had a working setup at one point that simply stopped. It took months of tinkering to figure out the issue. IIRC, in that case it came down to yahoo changing policies such that an app specific password had to be used and concurrently the certificates needed updating. I used gmail at that time for testing and I think it worked, but that was a long time back. Prior to the issues, I had been using email notification for a lot. But, since I found it troubling that a critical notification could be lost due to some certificate or policy update on the email server's side, I changed my approach.
I still wish I could get text message support back similar to how I had AHP setup. In that case, I used google voice to send/receive coded messages from my phone to control and report. It was really nice to be able to do that without worry of an instantaneous connection to the server. When it got through, it would do its thing. When it sent a message, it didn't matter if I was temporarily out of range. Right now, the app is good, but nothing like what I used to do.