I have two HC-801LTE trail cameras and one HC-810LTE trail camera. I wrote the review about them sometimes which is here. As I wrote there all of the cameras have an issue - after some time they stop sending pictures to email. When the camera is restarted the picture delivery is resumed.
In log file you see error lines:
2021/04/14 20:22:08 : AT+QFDEL="RAM:*"
2021/04/14 20:22:08 : +CME ERROR: 418
and
2021/04/14 20:22:12 : AT+QFUPL="RAM:PICT_20210414_2022.jpg",96238,200,1
2021/04/14 20:22:12 : +CME ERROR: 423
Based on the log file it seems that the camera is attaching the resized image from the memory - RAM:PICT_20210414_1715.jpg. In the case of a video file, the file is attached from the SD card - SD:\DCIM\100NVTIM\IMAG0045.mov.
I have long suspected that the camera has some sort of memory leak that causes the memory to fill. Since the images are also delivered from memory (RAM) this could be the cause of emails not being able to send after some time.
Since video files are delivered from an SD card this issue does not appear - the camera keeps sending the video files for much longer than image files. If you use VGA resolution and a 5-second video clip the file size is about 2,8MB. This is significantly larger than the image files, but at least the camera will not stop sending files after a few weeks.
I have tried to explain the problem to Suntek support but with no luck. All they tell me is to try different SMTP settings.