Here is a tutorial to unlock meizu E3 without any malicious software.
The idea is to edit frp partition and make the fastboot flashing unlock pass the security check.
Please note below might damage your phone so do it as your own risk, i do not responsible to any damage made.
(1)get root access
(2)install terminal emulater app
(3)dump frp partition
(4)modify frp by hex editor at offset 7fff8 and 7fff to 1 (not sure 7fff8 or 7ffff take the effect, so i edit both) as frp1
(5)write frp1 back to frp partition
(6)reboot boot loader
(7)fastboot flashing unlock
(8)press up-vol or down-vol (not sure, i stop here, feedback welcome)
This is generic enough for MTK and Qcom soc, success story other than sdm636 and mt6755 are welcome.
Other phone unlock tutorial:
Meizu M3note bootloader unlock