This is a small utility that logs outgoing email directly to a file. No SMTP, mail servers, or networking is involved.
Useful when you have a centralized log collector and want to keep records of outbound email in a scalable and searchable fashion.
See https://www.stackallocated.com/blog/2019/stop-using-smtp for more words about this.
This program only uses the Go standard library and should work with older versions of Go. It has been tested on Go 1.11 and later.
$ go build shim.go
$ sudo -s
# chown root:root shim
# chmod u+s shim
# mv shim /usr/sbin/sendmail
If you want to change the log filename, edit the line in shim.go.
$ /usr/sbin/sendmail [email protected]
Subject: Test
Hello World
^D
$ tail -1 /var/log/sendmail-shim.log.json
{"time":"2019-07-28T09:25:47Z","uid":"501","username":"hans","arguments":["[email protected]"],"body":"Subject: Test\n\nHello World\n"}
$
$ go test