We can manage email sending by .py (python) code.
To send an email in OpenERP using python code you can use the below code.

 import base64
import logging

from openerp import netsvc
from openerp.osv import osv, fields
from openerp.osv import fields
from openerp import tools
from openerp.tools.translate import _
from urllib import urlencode, quote as quote

_logger = logging.getLogger(__name__)

try:from jinja2.sandbox import SandboxedEnvironment
    mako_template_env = SandboxedEnvironment(
        block_start_string="<%",
        block_end_string="%>",
        variable_start_string="${",
        variable_end_string="}",
        comment_start_string="<%doc>",
        comment_end_string="",
        line_statement_prefix="%",
        line_comment_prefix="##",
        trim_blocks=True,               # do not output newline after blocks
        autoescape=True,                # XML/HTML automatic escaping
    )
    mako_template_env.globals.update({
        'str': str,
        'quote': quote,
        'urlencode': urlencode,
    })
except ImportError:
    _logger.warning("jinja2 not available, templating features will not work!")

class email_template(osv.osv):
    "Templates for sending email"
    _name = "email.template"
    _description = 'Email Templates'
    _order = 'name'

    def render_template(self, cr, uid, template, model, res_id, context=None):
        """Render the given template text, replace mako expressions ``${expr}``
           with the result of evaluating these expressions with
           an evaluation context containing:

                * ``user``: browse_record of the current user
                * ``object``: browse_record of the document record this mail is
                              related to
                * ``context``: the context passed to the mail composition wizard

           :param str template: the template text to render
           :param str model: model name of the document record this mail is related to.
           :param int res_id: id of the document record this mail is related to.
        """
        if not template:
            return u""
        if context is None:
            context = {}
        try:
            template = tools.ustr(template)
            record = None
            if res_id:
                record = self.pool.get(model).browse(cr, uid, res_id, context=context)
            user = self.pool.get('res.users').browse(cr, uid, uid, context=context)
            variables = {
                'object': record,
                'user': user,
                'ctx': context,     # context kw would clash with mako internals
            }
            result = mako_template_env.from_string(template).render(variables)
            if result == u"False":
                result = u""
            return result
        except Exception:
            _logger.exception("failed to render mako template value %r", template)
            return u""

    def get_email_template(self, cr, uid, template_id=False, record_id=None, context=None):
        if context is None:
            context = {}
        if not template_id:
            return False
        template = self.browse(cr, uid, template_id, context)
        lang = self.render_template(cr, uid, template.lang, template.model, record_id, context)
        if lang:
            # Use translated template if necessary
            ctx = context.copy()
            ctx['lang'] = lang
            template = self.browse(cr, uid, template.id, ctx)
        else:
            template = self.browse(cr, uid, int(template_id), context)
        return template

    def onchange_model_id(self, cr, uid, ids, model_id, context=None):
        mod_name = False
        if model_id:
            mod_name = self.pool.get('ir.model').browse(cr, uid, model_id, context).model
        return {'value': {'model': mod_name}}

    _columns = {
        'name': fields.char('Name'),
        'model_id': fields.many2one('ir.model', 'Applies to', help="The kind of document with with this template can be used"),
        'model': fields.related('model_id', 'model', type='char', string='Related Document Model',
                                size=128, select=True, store=True, readonly=True),
        'lang': fields.char('Language',
                            help="Optional translation language (ISO code) to select when sending out an email. "
                                 "If not set, the english version will be used. "
                                 "This should usually be a placeholder expression "
                                 "that provides the appropriate language, e.g. "
                                 "${object.partner_id.lang}.",
                            placeholder="${object.partner_id.lang}"),
        'user_signature': fields.boolean('Add Signature',
                                         help="If checked, the user's signature will be appended to the text version "
                                              "of the message"),
        'subject': fields.char('Subject', translate=True, help="Subject (placeholders may be used here)",),
        'email_from': fields.char('From',
            help="Sender address (placeholders may be used here). If not set, the default "
                    "value will be the author's email alias if configured, or email address."),
        'email_to': fields.char('To (Emails)', help="Comma-separated recipient addresses (placeholders may be used here)"),
        'email_recipients': fields.char('To (Partners)', help="Comma-separated ids of recipient partners (placeholders may be used here)"),
        'email_cc': fields.char('Cc', help="Carbon copy recipients (placeholders may be used here)"),
        'reply_to': fields.char('Reply-To', help="Preferred response address (placeholders may be used here)"),
        'mail_server_id': fields.many2one('ir.mail_server', 'Outgoing Mail Server', readonly=False,
                                          help="Optional preferred server for outgoing mails. If not set, the highest "
                                               "priority one will be used."),
        'body_html': fields.text('Body', translate=True, help="Rich-text/HTML version of the message (placeholders may be used here)"),
        'report_name': fields.char('Report Filename', translate=True,
                                   help="Name to use for the generated report file (may contain placeholders)\n"
                                        "The extension can be omitted and will then come from the report type."),
        'report_template': fields.many2one('ir.actions.report.xml', 'Optional report to print and attach'),
        'ref_ir_act_window': fields.many2one('ir.actions.act_window', 'Sidebar action', readonly=True,
                                            help="Sidebar action to make this template available on records "
                                                 "of the related document model"),
        'ref_ir_value': fields.many2one('ir.values', 'Sidebar Button', readonly=True,
                                       help="Sidebar button to open the sidebar action"),
        'attachment_ids': fields.many2many('ir.attachment', 'email_template_attachment_rel', 'email_template_id',
                                           'attachment_id', 'Attachments',
                                           help="You may attach files to this template, to be added to all "
                                                "emails created from this template"),
        'auto_delete': fields.boolean('Auto Delete', help="Permanently delete this email after sending it, to save space"),

        # Fake fields used to implement the placeholder assistant
        'model_object_field': fields.many2one('ir.model.fields', string="Field",
                                              help="Select target field from the related document model.\n"
                                                   "If it is a relationship field you will be able to select "
                                                   "a target field at the destination of the relationship."),
        'sub_object': fields.many2one('ir.model', 'Sub-model', readonly=True,
                                      help="When a relationship field is selected as first field, "
                                           "this field shows the document model the relationship goes to."),
        'sub_model_object_field': fields.many2one('ir.model.fields', 'Sub-field',
                                                  help="When a relationship field is selected as first field, "
                                                       "this field lets you select the target field within the "
                                                       "destination document model (sub-model)."),
        'null_value': fields.char('Default Value', help="Optional value to use if the target field is empty"),
        'copyvalue': fields.char('Placeholder Expression', help="Final placeholder expression, to be copy-pasted in the desired template field."),
    }

    _defaults = {
        'auto_delete': True,
    }

    def create_action(self, cr, uid, ids, context=None):
        vals = {}
        action_obj = self.pool.get('ir.actions.act_window')
        data_obj = self.pool.get('ir.model.data')
        for template in self.browse(cr, uid, ids, context=context):
            src_obj = template.model_id.model
            model_data_id = data_obj._get_id(cr, uid, 'mail', 'email_compose_message_wizard_form')
            res_id = data_obj.browse(cr, uid, model_data_id, context=context).res_id
            button_name = _('Send Mail (%s)') % template.name
            vals['ref_ir_act_window'] = action_obj.create(cr, uid, {
                 'name': button_name,
                 'type': 'ir.actions.act_window',
                 'res_model': 'mail.compose.message',
                 'src_model': src_obj,
                 'view_type': 'form',
                 'context': "{'default_composition_mode': 'mass_mail', 'default_template_id' : %d, 'default_use_template': True}" % (template.id),
                 'view_mode':'form,tree',
                 'view_id': res_id,
                 'target': 'new',
                 'auto_refresh':1
            }, context)
            vals['ref_ir_value'] = self.pool.get('ir.values').create(cr, uid, {
                 'name': button_name,
                 'model': src_obj,
                 'key2': 'client_action_multi',
                 'value': "ir.actions.act_window," + str(vals['ref_ir_act_window']),
                 'object': True,
             }, context)
        self.write(cr, uid, ids, {
                    'ref_ir_act_window': vals.get('ref_ir_act_window',False),
                    'ref_ir_value': vals.get('ref_ir_value',False),
                }, context)
        return True

    def unlink_action(self, cr, uid, ids, context=None):
        for template in self.browse(cr, uid, ids, context=context):
            try:
                if template.ref_ir_act_window:
                    self.pool.get('ir.actions.act_window').unlink(cr, uid, template.ref_ir_act_window.id, context)
                if template.ref_ir_value:
                    ir_values_obj = self.pool.get('ir.values')
                    ir_values_obj.unlink(cr, uid, template.ref_ir_value.id, context)
            except Exception:
                raise osv.except_osv(_("Warning"), _("Deletion of the action record failed."))
        return True

    def unlink(self, cr, uid, ids, context=None):
        self.unlink_action(cr, uid, ids, context=context)
        return super(email_template, self).unlink(cr, uid, ids, context=context)

    def copy(self, cr, uid, id, default=None, context=None):
        template = self.browse(cr, uid, id, context=context)
        if default is None:
            default = {}
        default = default.copy()
        default.update(
            name=_("%s (copy)") % (template.name),
            ref_ir_act_window=False,
            ref_ir_value=False)
        return super(email_template, self).copy(cr, uid, id, default, context)

    def build_expression(self, field_name, sub_field_name, null_value):
        """Returns a placeholder expression for use in a template field,
           based on the values provided in the placeholder assistant.

          :param field_name: main field name
          :param sub_field_name: sub field name (M2O)
          :param null_value: default value if the target value is empty
          :return: final placeholder expression
        """
        expression = ''
        if field_name:
            expression = "${object." + field_name
            if sub_field_name:
                expression += "." + sub_field_name
            if null_value:
                expression += " or '''%s'''" % null_value
            expression += "}"
        return expression

    def onchange_sub_model_object_value_field(self, cr, uid, ids, model_object_field, sub_model_object_field=False, null_value=None, context=None):
        result = {
            'sub_object': False,
            'copyvalue': False,
            'sub_model_object_field': False,
            'null_value': False
            }
        if model_object_field:
            fields_obj = self.pool.get('ir.model.fields')
            field_value = fields_obj.browse(cr, uid, model_object_field, context)
            if field_value.ttype in ['many2one', 'one2many', 'many2many']:
                res_ids = self.pool.get('ir.model').search(cr, uid, [('model', '=', field_value.relation)], context=context)
                sub_field_value = False
                if sub_model_object_field:
                    sub_field_value = fields_obj.browse(cr, uid, sub_model_object_field, context)
                if res_ids:
                    result.update({
                        'sub_object': res_ids[0],
                        'copyvalue': self.build_expression(field_value.name, sub_field_value and sub_field_value.name or False, null_value or False),
                        'sub_model_object_field': sub_model_object_field or False,
                        'null_value': null_value or False
                        })
            else:
                result.update({
                        'copyvalue': self.build_expression(field_value.name, False, null_value or False),
                        'null_value': null_value or False
                        })
        return {'value': result}

    def generate_email(self, cr, uid, template_id, res_id, context=None):
        """Generates an email from the template for given (model, res_id) pair.

           :param template_id: id of the template to render.
           :param res_id: id of the record to use for rendering the template (model
                          is taken from template definition)
           :returns: a dict containing all relevant fields for creating a new
                     mail.mail entry, with one extra key ``attachments``, in the
                     format [(report_name, data)] where data is base64 encoded.
        """
        if context is None:
            context = {}
        report_xml_pool = self.pool.get('ir.actions.report.xml')
        template = self.get_email_template(cr, uid, template_id, res_id, context)
        ctx = context.copy()
        if template.lang:
            ctx['lang'] = template._context.get('lang')
        values = {}
        for field in ['subject', 'body_html', 'email_from',
                      'email_to', 'email_recipients', 'email_cc', 'reply_to']:
            values[field] = self.render_template(cr, uid, getattr(template, field),
                                                 template.model, res_id, context=ctx) \
                                                 or False
        if template.user_signature:
            signature = self.pool.get('res.users').browse(cr, uid, uid, context).signature
            if signature:
                values['body_html'] = tools.append_content_to_html(values['body_html'], signature)

        if values['body_html']:
            values['body'] = tools.html_sanitize(values['body_html'])

        values.update(mail_server_id=template.mail_server_id.id or False,
                      auto_delete=template.auto_delete,
                      model=template.model,
                      res_id=res_id or False)

        attachments = []
        # Add report in attachments
        if template.report_template:
            report_name = self.render_template(cr, uid, template.report_name, template.model, res_id, context=ctx)
            report_service = 'report.' + report_xml_pool.browse(cr, uid, template.report_template.id, context).report_name
            # Ensure report is rendered using template's language
            service = netsvc.LocalService(report_service)
            (result, format) = service.create(cr, uid, [res_id], {'model': template.model}, ctx)
            # TODO in trunk, change return format to binary to match message_post expected format
            result = base64.b64encode(result)
            if not report_name:
                report_name = report_service
            ext = "." + format
            if not report_name.endswith(ext):
                report_name += ext
            attachments.append((report_name, result))

        attachment_ids = []
        # Add template attachments
        for attach in template.attachment_ids:
            attachment_ids.append(attach.id)

        values['attachments'] = attachments
        values['attachment_ids'] = attachment_ids
        return values

    def send_mail(self, cr, uid, template_id, res_id, force_send=False, context=None):
        """Generates a new mail message for the given template and record,
           and schedules it for delivery through the ``mail`` module's scheduler.

           :param int template_id: id of the template to render
           :param int res_id: id of the record to render the template with
                              (model is taken from the template)
           :param bool force_send: if True, the generated mail.message is
                immediately sent after being created, as if the scheduler
                was executed for this message only.
           :returns: id of the mail.message that was created
        """
        if context is None:
            context = {}
        mail_mail = self.pool.get('mail.mail')
        ir_attachment = self.pool.get('ir.attachment')

        # create a mail_mail based on values, without attachments
        values = self.generate_email(cr, uid, template_id, res_id, context=context)
        if not values.get('email_from'):
            raise osv.except_osv(_('Warning!'),_("Sender email is missing or empty after template rendering. Specify one to deliver your message"))
        # process email_recipients field that is a comma separated list of partner_ids -> recipient_ids
        # NOTE: only usable if force_send is True, because otherwise the value is
        # not stored on the mail_mail, and therefore lost -> fixed in v8
        recipient_ids = []
        email_recipients = values.pop('email_recipients', '')
        if email_recipients:
            for partner_id in email_recipients.split(','):
                if partner_id:  # placeholders could generate '', 3, 2 due to some empty field values
                    recipient_ids.append(int(partner_id))

        attachment_ids = values.pop('attachment_ids', [])
        attachments = values.pop('attachments', [])
        msg_id = mail_mail.create(cr, uid, values, context=context)
        mail = mail_mail.browse(cr, uid, msg_id, context=context)

        # manage attachments
        for attachment in attachments:
            attachment_data = {
                'name': attachment[0],
                'datas_fname': attachment[0],
                'datas': attachment[1],
                'res_model': 'mail.message',
                'res_id': mail.mail_message_id.id,
            }
            context.pop('default_type', None)
            attachment_ids.append(ir_attachment.create(cr, uid, attachment_data, context=context))
        if attachment_ids:
            values['attachment_ids'] = [(6, 0, attachment_ids)]
            mail_mail.write(cr, uid, msg_id, {'attachment_ids': [(6, 0, attachment_ids)]}, context=context)

        if force_send:
            mail_mail.send(cr, uid, [msg_id], recipient_ids=recipient_ids, context=context)
        return msg_id

Hope example is stated above helps you. :)