I just got a notification that I'm not allowed to send any more emails from my EC2 instance. Which is a bit perplexing since I wasn't aware that I was sending any. Is there some way for me to have a look at the emails, or at least check which applications tried to send emails? I'm on ubuntu.
On Linux, from and to addresses of mail are typically logged by the default settings of most mail packages.
Try looking in /var/log/mail.log, or /var/log/syslog, or, if that doesn't help,
grep 'to=<' /var/log/* | less
The actual mail itself may not be available.
Remember, mail is pretty easy to fake. It may not be coming from your machine. But if you are not sending mail from your machine and want to eliminate the possibility, consider uninstalling any mail software and/or blocking ports like smtp/25 in your firewall settings.