I think I have a Gmail account but never use it but I'll give it a go to see if that makes any difference. I'll confirm if anything changes in due course. Two points why I don't think it will make any difference:
1. I still don't understand why, if these are genuine event-triggered emails, they do not also trigger recording, since all other "readable" emails with picture attachments do trigger recording. I don't suppose Hikvision support made any mention about that?
2. I was looking at live stream on the Hik-connect app on my phone earlier this morning when one of these odd emails came through and there was no reason for an email to be generated during the time I was looking at it, i.e. nothing passed within sight of the camera to trigger any events for the time-stamp on the email.
I got about 12 of these overnight and have had a similar amount of them today so far.