Here is the part of the log file that shows to messages first one [14] to a partner (not arrived) and second [15] to a user (arrived).
2016-06-18 13:01:24,906 22130 INFO moneygrid_net werkzeug: 10.10.0.1 - - [18/Jun/2016 13:01:24] "POST /web/dataset/call_kw/res.partner/message_get_suggested_recipients HTTP/1.0" 200 -
2016-06-18 13:01:33,093 22130 INFO moneygrid_net openerp.addons.mail.models.mail_mail: Mail with ID 14 and Message-Id u'<1466254892.473463058471680.080799568425410-openerp-8-res.partner@host-odoo-1>' successfully sent
2016-06-18 13:01:33,098 22130 INFO moneygrid_net openerp.models.unlink: User #1 deleted mail.mail records with IDs: [14]
2016-06-18 13:01:33,150 22130 INFO moneygrid_net werkzeug: 10.10.0.1 - - [18/Jun/2016 13:01:33] "POST /web/dataset/call_kw/res.partner/message_post HTTP/1.0"
2016-06-18 13:01:55,876 22130 INFO moneygrid_net werkzeug: 10.10.0.1 - - [18/Jun/2016 13:01:55] "POST /longpolling/pollHTTP/1.0" 200 -
2016-06-18 13:02:45,958 22130 INFO moneygrid_net werkzeug: 10.10.0.1 - - [18/Jun/2016 13:02:45] "POST /longpolling/poll
2016-06-18 13:04:20,631 22130 INFO moneygrid_net werkzeug: 10.10.0.1 - - [18/Jun/2016 13:04:20] "POST /web/dataset/call_kw/res.partner/message_get_suggested_recipients HTTP/1.0" 200 -
2016-06-18 13:04:24,761 22130 INFO moneygrid_net openerp.addons.mail.models.mail_mail: Mail with ID 15 and Message-Id u'<1466255064.221683025360107.027978441168077-openerp-6-res.partner@host-odoo-1>' successfully sent
2016-06-18 13:04:24,765 22130 INFO moneygrid_net openerp.models.unlink: User #1 deleted mail.mail records with IDs: [15]
2016-06-18 13:04:24,806 22130 INFO moneygrid_net werkzeug: 10.10.0.1 - - [18/Jun/2016 13:04:24] "POST /web/dataset/call_kw/res.partner/message_post HTTP/1.0" 200 -
Do you have any error messages in the log?