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Predicate smtp_send_mail/3
 smtp_send_mail(+To, :Goal, +Options)
Send mail using SMTP. To is the e-mail address of the receiver. Options:
  • smtp(+Host) the name or ip address for smtp host, eg. swi-prolog.org
  • from(+FromAddress) atomic identifies sender address. Provides the default for header(from(From)).
  • date(+Date) Set the date header. Default is to use the current time.
  • subject(+Subject) atomic: text for 'Subject:' email header
  • auth(User-Password) authentication credentials, as atoms or strings.
  • auth_method(+PlainOrLoginOrNone) type of authentication. Default is default, alternatives are plain and login
  • security(Security) one of: none, ssl, tls, starttls
  • content_type(+ContentType) sets Content-Type header
  • mailed_by(By) add X-Mailer: SWI-Prolog <version>, pack(smtp) to header iff By == true
  • header(Name(Val)) add HName: Val to headers. HName is Name if Name's first letter is a capital, and it is Name after capitalising its first letter otherwise. For instance header(from('My name, me@server.org')) adds header "From: My name, my@server.org" and header('FOO'(bar)) adds "FOO: bar"

Defaults are provided by settings associated to this module.

Listens to debug(smtp) which for instance reports failure to connect, (computation fails as per non-debug execution).

Arguments:
To- is an atom holding the target address
Goal- is called as call(Goal, Stream) and must provide the body of the message.
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Jon Judge said (2017-01-08T16:53:51):0 upvotes 0 0 downvotes
Picture of user Jon Judge.

Using smtp_send_mail/3 with DKIM signature verification

Re: from(+FromAddress) atomic identifies sender address (does not set From: header)

Since from() does not set the header, dkim will fail within your mail server with eg:

Jan  8 16:29:53 host opendkim[2190]: v08GTpuZ002463: can't determine message sender; accepting
Jan  8 16:29:53 host sm-mta[2463]: v08GTpuZ002463: milter=opendkim, action=eoh, continue
Jan  8 16:29:53 host sm-mta[2463]: v08GTpuZ002463: milter=opendkim, action=body, skip
Jan  8 16:29:53 host sm-mta[2463]: v08GTpuZ002463: Milter insert (1): header: Authentication-Results: host.example.com; dkim=permerror (bad message/signature format)

On your email client, the email message source headers will contain:

Authentication-Results:host.example.com; dkim=permerror (bad message/signature format)

To fix this, you need to add an extra header (last param below) which is a copy of the from() information,

smtp_send_mail :-
        compose_message,
        [ subject('some subject'),
          from('Joe <joe@example.com>'),
          smtp('host.example.com'),
          auth('username'-'SuperSecretPassword'),
          auth_method(plain),
          content_type('text/html; charset=utf-8;'),
          security(starttls),
            
          % needed for dkim, since from() above doesn't set From: header
          header('From'('Joe <joe@example.com>'))
        ]).

Then the email server will report a correct signature check:

Jan  8 16:49:58 host sm-mta[2602]: v08GntQt002602: Milter insert (1): header: DKIM-Signature:  v=1; a=rsa-sha256; c=simple/simple; d=example.com;\n\ts=201612191203; t=1483894198;\n\tbh=gwXbMF85dCqPD8lC3d6mcSAFjffFHIYVBZecFIccdX4=;\n\th=To:From:List-Unsubscribe:Reply-To:Subject:From;\n\tb=rCfD49c3Gf3FUlnko6lY/aJE9Uzp8KY73gjU5D3ebc05vsEC9xy9yZsGG0F8v1UP9\n\t SC/du993+VWqbvyRZorTp+MbKhvM4y/VA2Kg2MbIkK/YAeuhRo2zMHpMRKlz6awf2Z\n\t 3h5bo62LFFBFXMM3cN+7QeiVOQegqmup+xtRlS5M=

Client:

DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=example.com;
      s=201612191203; t=1483893267;
      bh=vMvc1m8dEiZTVtf4Vhr6fw94boBpQlS+alJ8NzfjjYw=;
      h=To:From:Reply-To:Subject:From;
      b=S8JZBRioLkhkHrcoX00rVaoI4nHfLK/8n3CuiHAW0Cx3vmkJDl8+NEVOsIVSnwWqK
       PPBBp7dVMngCoh9uPT1I4gVjJZXGdqgXjDpRg4EXq/+peyAUYI/IWMEN181rz2dE1I
       MSpgPu9Pdh0JOQVZsYCbYNYINQHYjXnIx808ZP0w=