linux - How to create an email file? -

after fetchmail fetches mails, new mails stored in file /var/mail/user. can open file user text editor vim.

how can create such text-based email files? say, want send email contents:

from: sender <sender@xx.com>  to: receiver <receiver@xx.com> subject: test subject contents: ... attached: file1.txt, file2.png, file3.pdf 

the problem how make these formal text-based email.

besides, if have such email file. how can extract files(say, subjects, contents, attached files, etc.) command line tools. know can open program mutt. can done using command line utility?

there bunch of standards need understand, email fundamentally text.

the file format in /var/spool/mail or /var/mail/user etc typically berkeley mbox. not formally defined anywhere, consists of sequence of rfc5322 (née rfc822) email messages, each preceded from_ line, format of from %s %c %s sender's email address (what see in return-path:) , %c date when message arrived. notice 2 spaces between format strings!

the toplevel email message rfc5322 on top of that, need understand mime.

• mbox: rfc 4155
• email message format: rfc5322
• mime: rfc2045 rfc2046 rfc2047 rfc2048

you stumble on (e)smtp rfc5321 tangential question, know. notice how 821 , 822 (and later 2821 , 2822, , 5321 , 5322) have adjacent rfc numbers.

furthermore, there wild, wild west of non-standard headers, of nonetheless significant. dan bernstein's reference http://cr.yp.to/immhf.html lifesaver. general guideline, spammers typically copy/paste headers without understanding them; therefore, essential practice deliverability "don't that". in other words, if don't know header for, don't use it.

any modern programming language come libraries create , manipulate rfc5322 , mime, , mbox too. creating message can send somewhere, don't need mbox anyway, along lines of (pseudocode)

message = new mime({'subject': 'hello', 'from': 'me@example.net',                    'to': 'my friend <you@example.com>'}); message.addbodypart('text/plain', 'hi fred.\nhow you?'); message.addbodypart('image/png', {'file': '/home/you/logo.png'});  smtp = new smtp('mail.example.net', 587, {'user': 'me', 'pass': 'xyzzy'}); smtp.send(message); 

a multipart message looks describe in question, except there no specific header identify "attachments" , conceptually no "attachments", "body parts". here simple mime message show message in question like.

from: sender <sender@example.com>  to: receiver <receiver@example.com> subject: test subject mime-version: 1.0 content-type: multipart/mixed; boundary="so_long_eflop"  mime multipart message.  nobody sees says here.  --so_long_eflop content-type: text/plain; charset="utf-8" content-disposition: inline content-transfer-encoding: 7bit  many mail clients display "main part" mime not define particular hierarchy.  many mail clients generate text/plain rendering , text/html rendering of message type in, , recipient's mail client decide -- based on user preferences -- 1 display.  anyway, not create example of here.  "a text message picture attached", or, more precisely, mime message 2 body parts.  oh, content-disposition: inline implied text/plain part.  clients override or ignore disposition set sender anyway.  --so_long_eflop content-type: image/png content-disposition: attachment content-transfer-encoding: base64  iam+not/attaching+a/real00picture+here/just/a/bunch0of/binary/goo===  --so_long_eflop--