Sending email
Sending email with curl is done with the SMTP protocol. SMTP stands for Simple Mail Transfer Protocol.
curl supports sending data to an SMTP server, which combined with the right set of command line options makes an email get sent to a set of receivers of your choice.
When sending SMTP with curl, there are two necessary command line options that must be used.
-
You need to tell the server at least one recipient with
--mail-rcpt. You can use this option several times and then curl will tell the server that all those email addresses should receive the email. -
You need to tell the server which email address that is the sender of the email with
--mail-from. It is important to realize that this email address is not necessarily the same as is shown in theFrom:line of the email text.
Then, you need to provide the actual email
data. This is a (text) file formatted
according to
RFC 5322. It is a set of headers and a body. Both
the headers and the body need to be
correctly encoded. The headers typically
include To:, From:, Subject:, Date:
etc.
A basic command to send an email:
curl smtp://mail.example.com --mail-from [email protected] --mail-rcpt[email protected] --upload-file email.txt
From: John Smith <[email protected]>To: Joe Smith <[email protected]>Subject: an example.com example emailDate: Mon, 7 Nov 2016 08:45:16​Dear Joe,Welcome to this example email. What a lovely day.
Some mail providers allow or require using SSL for SMTP. They may use a dedicated port for SSL or allow SSL upgrading over a clear-text connection.
If your mail provider has a dedicated SSL port you can use smtps:// instead of smtp://, which uses the SMTP SSL port of 465 by default and requires the entire connection to be SSL. For example smtps://smtp.gmail.com/.
However, if your provider allows upgrading from clear-text to secure transfers you can use one of these options:
--ssl Try SSL/TLS (FTP, IMAP, POP3, SMTP)--ssl-reqd Require SSL/TLS (FTP, IMAP, POP3, SMTP)
You can tell curl to try
but not require upgrading to secure
transfers by adding --ssl
to the command:
curl --ssl smtp://mail.example.com --mail-from [email protected]--mail-rcpt [email protected] --upload-file email.txt--user '[email protected]:your-account-password'
You can tell curl to require
upgrading to using secure transfers by
adding --ssl-reqd
to the command:
curl --ssl-reqd smtp://mail.example.com --mail-from [email protected]--mail-rcpt [email protected] --upload-file email.txt--user '[email protected]:your-account-password'
The path part of a SMTP request specifies the host name to present during communication with the mail server. If the path is omitted then curl will attempt to figure out the local computer's host name and use that. However, this may not return the fully qualified domain name that is required by some mail servers and specifying this path allows you to set an alternative name, such as your machine's fully qualified domain name, which you might have obtained from an external function such as gethostname or getaddrinfo.
To connect to the mail server at mail.example.com
and send your local computer's host
name in the HELO / EHLO command:
curl smtp://mail.example.com
You can of course as always use the -v
option to get to see the client-server
communication.
To instead have curl send client.example.com
in the HELO
/ EHLO
command to the mail server at mail.example.com, use:
curl smtp://mail.example.com/client.example.com
When you send email with an ordinary mail
client, it will first check for an MX record
for the particular domain you want to send
email to. If you send an email to
[email protected], the client will get the MX records for example.com
to learn which mail server(s) to use when
sending email to example.com users.
curl does no MX lookups by itself. If you want to figure out which server to send an email to for a particular domain, we recommend you figure that out first and then call curl to use those servers. Useful command line tools to get MX records include 'dig' and 'nslookup'.
