Since the 4.7.8 update to 4.7.10 and 4.7.10 to 4.7.12 recently some mails are not reaching their recipients. If I look at the Mailing Detail Report the Successful Deliveries rate is between 90% and 100% and the status of the not received mails are "Unknown".
To see these mails on the report I have to filter as status "-any-" because there is no possibility to do it with the status "unknown".
Has anyone encountered the same problem? What may be due?
I investigated a little more and I see that "Unknown" status appears when there is no record on the civicrm_mailing_event_bounce table AND when there is no record on the civicrm_mailing_event_delivered. Then, it seems that for some users, there isn't registering the delivery of the mail.
I begin to suspect that the problem is related with an issue of inconsitency caches of the mailing recipients groups.
I found on logs messages like
[info] CiviMail will not send an empty mail body, Skipping: firstname.lastname@example.org corresponding to the contacts with mailing status marked as "Unknown".