Setting headers using the /bin/mail command

emailmail-command

I have a bash script that I use with nagios that sends notifications by email. The key part of it looks like this:

# $1 (FROM) | $2 (TO) | $3 (SUBJECT) | $4 (BODY)
/usr/bin/printf "%b" "$4" | /bin/mail -s "$3" "$2" -- -f $1

I know I could use the sendmail command directly (like this) but it would mean reworking a few scripts to take care of building the entire message including all headers.

Is there any way to specify additional SMTP headers using /bin/mail, in my own case I am trying to add the Importance: high header?

I'm running exim 4.63 as my MTA and CentOS 5.6 x64.

Best Answer

There are many different versions of mail (see Mail vs. mail what is the difference and the Heirloom project's write-up on the different versions of mail).

If you want to keep your sanity, I recommend avoiding any tool whose name is too close to mail. Mutt is a lean text mode mail client which is often available, very flexible, and behaves the same everywhere.

mutt -H - "$2" <<EOF
From: $1
To: $2
Subject: $3
Importance: high

$4
EOF

Related Solutions

How to send HTML email using linux ‘mail’ command

There are many different versions of mail around. When you go beyond mail -s subject to1@address1 to2@address2 <body (for sending, that's all POSIX guarantees — and even -s didn't exist in the old days), they tend to have different command line options. Adding an additional header isn't always easy.

With some mailx implementations, e.g. from mailutils on Ubuntu or Debian's bsd-mailx, it's easy, because there's an option for that.
```
mailx -a 'Content-Type: text/html' -s "Subject" to@address <test.html
```

With the Heirloom mailx, there's no convenient way. One possibility to insert arbitrary headers is to set editheaders=1 and use an external editor (which can be a script).

## Prepare a temporary script that will serve as an editor.
## This script will be passed to ed.
temp_script=$(mktemp)
cat <<'EOF' >>"$temp_script"
1a
Content-Type: text/html
.
$r test.html
w
q
EOF
## Call mailx, and tell it to invoke the editor script
EDITOR="ed -s $temp_script" heirloom-mailx -S editheaders=1 -s "Subject" to@address <<EOF
~e
.
EOF
rm -f "$temp_script"

With a general POSIX mailx, I don't know how to get at headers.

If you're going to use any mail or mailx, keep in mind that

This isn't portable even within a given Linux distribution. For example, both Ubuntu and Debian have several alternatives for mail and mailx.
When composing a message, mail and mailx treats lines beginning with ~ as commands. If you pipe text into mail, you need to arrange for this text not to contain lines beginning with ~.

If you're going to install software anyway, you might as well install something more predictable than mail/Mail/mailx. For example, mutt. With Mutt, you can supply most headers in the input with the -H option, but not Content-Type, which needs to be set via a mutt option.

mutt -e 'set content_type=text/html' -s 'hello' 'to@address' <test.html

Or you can invoke sendmail directly. There are several versions of sendmail out there, but they all support sendmail -t to send a mail in the simplest fashion, reading the list of recipients from the mail. (I think they don't all support Bcc:.) On most systems, sendmail isn't in the usual $PATH, it's in /usr/sbin or /usr/lib.

cat <<'EOF' - test.html | /usr/sbin/sendmail -t
To: to@address
Subject: hello
Content-Type: text/html

EOF

Mail vs. mail what is the difference

Historically, there have been many incompatible extensions of the original mail commnad. Mail came from BSD, and took the name Mail rather than mail because it was shipped alongside the incompatible mail program. Later the same story happened with mailx. For more details, read the Heirloom project's write-up on the different versions of mail. Linux distributions have variously provided one or more of the mail utilities under various names.

For portability, even between installations of the same Linux distribution sometimes, you can't rely on mail. The mailx command is standardized (not with all the options that might exist on a particular system).

If you want a utility that always behaves in the same way provided it's present, and you don't mind that it's often not installed by default, you can use mutt.

Best Answer

Related Solutions

How to send HTML email using linux ‘mail’ command

Mail vs. mail what is the difference

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