New: emailing with curl notes

notes/shell/email_with_curl.md

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+# Emailing with Curl
+
+`curl` is an amazing networking tool. It can even automate sending emails!
+You'll need a app password or real password to login to your email account
+
+## Email just a file
+
+For the most basic email, we can stuff the headers into the email file itself.
+Here's a basic example
+
+```bash
+cat <<EMAIL email.txt
+From: Emiliko Mirror <emiliko@gmail.com>
+To: Emiliko Mirror <emiliko@cs.ox.ac.uk>
+Subject: Sleep triggered on $(hostname)
+Date: $(date)
+
+Dear me,
+
+The system went to sleep! I thought I should notify my gmail account, so here
+I am.
+
+cheers,
+Emiliko
+EMAIL
+
+curl --silent --ssl-reqd \
+  --url 'smtps://smtp.gmail.com:465' \
+  --user 'emiliko@cs.ox.ac.uk:<my-password-here>' \
+  --mail-from 'emiliko@cs.ox.ac.uk' \
+  --mail-rcpt 'emiliko@gmail.com' \
+  --upload-file email.txt
+```
+
+The `From:` - `Date:` headers at the top are very important. Gmail seems to
+insert them automatically if they're missing, though other mail providers
+require them
+
+If you use 2fa, you'll need to [obtain an app
+password](https://support.google.com/accounts/answer/185833?hl=en) instead
+
+## Email with attachments
+
+We can also `CC`, `BCC` and attach files with our curl emails
+
+Attachments need a MIME type for the file, which is easiest obtained with the
+`file` command. In this example, we also remove the headers from the email file,
+opting to use the more explicit `-H` curl option
+
+```bash
+declare -r attach_file=mirrors_house.png
+declare -r mime_type="$(file --mime-type "$attach_file" | sed 's/.*: //')"
+
+cat <<EMAIL >email.txt
+Dear classmates,
+
+I just bought a new house! Check out the picture I attached below
+
+OMGOMGOMG, I'm so excited!
+
+cheers,
+Kate Mirror
+EMAIL
+
+curl --silent --ssl-reqd \
+  --url 'smtps://smtp.fastmail.com:465' \
+  --user 'kate%40mirror.house:<my-password>' \
+  --mail-from "kate@mirror.house" \
+  --mail-rcpt 'emiliko@cs.ox.ac.uk' \
+  --mail-rcpt 'lou@lou.me' \
+  --mail-rcpt 'louis@louis.me' \
+  -F '=(;type=multipart/mixed' \
+  -F "=$(cat email.txt);type=text/plain" \
+  -F "file=@${attach_file};filename=home.png;type=${mime_type};encoder=base64" \
+  -F '=)' \
+  -H "From: Kate Mirror <kate@mirror.house>" \
+  -H "Subject: Check out my new place!" \
+  -H "To: Emiliko Mirror <emiliko@cs.ox.ac.uk>" \
+  -H "CC: Lou Mirror <lou@lou.me>" \
+  -H "Date: $(date)"
+```
+
+Notice that for `BCC` the user isn't mentioned in `-H` at all, though still gets
+a `--mail-rcpt`
+
+Oddly, some mail servers seem sensitive to the filename field. My university
+server would consistently bounce emails when I tried to have a filename field.
+Consider removing it to use the file's actual name
+
+## Further reading
+
+ - [A basic official guide](https://everything.curl.dev/usingcurl/smtp)
+ - [Sending a simple email with
+   curl](https://stackoverflow.com/questions/14722556/using-curl-to-send-email)
+ - [An example on using the -F option with
+   curl](https://blog.ambor.com/2021/08/using-curl-to-send-e-mail-with.html)
+ - [Backup of the above on
+   github](https://github.com/ambanmba/send-ses/blob/main/send-ses.sh)
+ - [A hit at using the filename field in
+   forums](https://stackoverflow.com/questions/15127732/change-name-of-upload-file-in-curl)