I'm using HTML::Template for templating, MIME::Base64 for encode_base64, Email::Date::Format for email_date.

Template:

To: <!-- TMPL_VAR TO -->
From:  <!-- TMPL_VAR FROM -->
Subject: =?UTF-8?B?<!-- TMPL_VAR SUBJECT -->?=
Message-ID: <<!-- TMPL_VAR MSGID -->>
<!-- TMPL_IF NAME="DATE" -->Date:  <!-- TMPL_VAR DATE --><!-- /TMPL_IF
+ -->
MIME-Version: 1.0
Content-Type: multipart/mixed;
 boundary="------------<TMPL_VAR BOUNDARY>"
Content-Language: ru

This is a multi-part message in MIME format.
--------------<TMPL_VAR BOUNDARY>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit

<TMPL_VAR TEXT>

--
signature

<TMPL_IF ATTACHMENTS>
<TMPL_LOOP ATTACHMENTS>
--------------<TMPL_VAR BOUNDARY>
Content-Type: <TMPL_VAR FILETYPE>;
 name="<TMPL_VAR FILENAME>"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename="<TMPL_VAR FILENAME>"

<TMPL_VAR FILEBASE64>
</TMPL_LOOP>


</TMPL_IF>
--------------<TMPL_VAR BOUNDARY>--
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Email code:

               
my $email_params = {
  to => $email,
  from => 'robot@domain.ru',
  subject => encode_base64('Subject',''),
  text => 'Mail text',
  boundary => encode_base64($email,''),
  date => email_date(time);,
  msgid => encode_base64($email.$date,'').'@domain.ru',
};

foreach my $d (sort keys %{$email_docs} ) {
  push @{ $email_params->{attachments}}, {
    FILEBASE64 => encode_base64($d->pdf), # binary
    FILENAME => $d->filename_pdf,
    FILETYPE => "application/pdf",
  }
}

my $tpl = new HTML::Template(filename => $template);
$tpl->param($email_params);

open(my $MAIL, "|/usr/local/bin/sudo /usr/sbin/sendmail -t");
print $MAIL $tpl->output;
close ($MAIL);
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