It seems you are referring to this support page about uploading footage using SMTP:
https://www.cameraftp.com/Camera/CloudRecordingWithNestcam_Dropcam_Alternative.html
If your camera supports FTP (FTPS/SFTP), it is recommended using FTP. Otherwise, you can try SMTP.
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Your SMTP configuration is mostly right. There are two issues:
(1) Please use cftpMailUploader.drivehq.com as the email server instead of m.cameraftp.com.
(2) The sender email address should be in this format: cftp_USERNAME_CameraFolderID@ANY_DOMAIN.com. In your case, you used cftp_RNN_3521795@a.com, which is almost correct. However, I noticed that 3521795 is actually your camera name, not your camera folder ID.
To find a camera's folder ID, please go to My Cameras page, click the gear icon below your camera thumbnail. It will go to a page with the following URL:
https://www.cameraftp.com/Camera/EditCamera.aspx?action=load&folderID=##########
here ########## is your camera folder ID.