On a well established site that uses CiviMail and Groups for a range of mailing lists, a message was sent out this morning as usual to a list of over 1400 people.
Inexplicably, each recipient received the mail 4 times. I have checked and the message was definitely only queued once, and was sent out by a single cron job. The report for the message makes clear that something very odd happened:
Intended Recipients 1411 Successful Deliveries 5644 (400.00%) Tracked Opens 268 Click-throughs 50 [...] Scheduled Date May 20th, 2015 9:48 AM Status Complete Start Date May 20th, 2015 10:00 AM End Date May 20th, 2015 10:11 AM
Normally a cron such as this takes about 2 minutes to run. This one took substantially longer.
The CiviCRM installation was upgraded to the latest version on May 4th, however multiple messages have been sent successfully in the interim.
I cannot see any evidence of user error which would have caused this to occur.
Greatly appreciate any thoughts on how this came about, as the site owners are naturally reluctant to use the system again until the cause has been established.