Came into the office this morning to be greeted by 7440 blank email alerts from our 3 month old 2860ac.
It has the current firmware installed

Syslog shows repeated attempts at connecting to ddns even though the ddns is unconfigured and disabled.
I disabled email alerts and yet they keep coming

Syslog :

2017-05-16 16:46:10 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:46:00 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:45:49 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:45:39 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:45:34 Email send Failed.
2017-05-16 16:45:28 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:45:18 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:45:07 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:44:57 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:44:46 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:44:40 Email send Failed.
2017-05-16 16:44:36 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:44:33 Email send Failed.
2017-05-16 16:44:25 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:44:20 Email send Failed.
2017-05-16 16:44:15 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:44:14 Email send Failed.
2017-05-16 16:44:04 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:43:54 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:43:43 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:43:33 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:43:22 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:43:21 Email send Failed.
2017-05-16 16:43:12 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:43:01 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:42:51 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:42:40 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:42:30 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:42:19 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:42:18 Email send Failed.
2017-05-16 16:42:09 Email send Failed.
2017-05-16 16:42:09 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:41:58 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:41:56 Email send Failed.
2017-05-16 16:41:49 Email send Failed.
2017-05-16 16:41:48 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:41:37 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:41:27 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:41:16 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:41:06 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:40:55 [WEB]Dynamic DNS Setup> Force Update
2017-05-16 16:40:45 Email send Failed.
2017-05-16 16:40:45 [WEB]Dynamic DNS Setup> Force Update

I have just done a factory reset at the rest button on the front of the unit.
Updated firmware to v2860_3844_BT
Reloaded config from backup

No difference,
Faults are:
Email on every time dynamic dns forces update (DDNS is not configured or enabled)
Unit will not recognise attached USB memory stick (confirmed working on 3 separate pc's)
Cannot see firewall logs other than "USER" -

Anybody from Draytek on these forums???????

No, DrayTek don't have staff here.

Given those faults I would create a support ticket , that will get you the attention you need from DrayTek.

Thanks Adrian

I opened a ticket on Friday - just only had an acknowledgement this morning ....
22,200 emails over the weekend - not good
I had this with a previous 2860n+ and disabling the mail alert function stopped it, but not this time - firmware bug perhaps