“The mail could not be sent to the recipients because of the mail server failure. (Sending Mail using Account 1 (YYYY-MM-DDTHH:MM:SS). Exception Message: Could not write to temp attachment file. (There is not enough space on the disk)”
You may experience such an error when trying to send an attached email using Database Mail.
If you do not have enough space on your System Disk (the disk where the Operating System is running), you will encounter this error. Make sure that there is enough free space on your system disk (which is usually C:).