Sony Mobile recently released a new update for the Xperia M5 series, which moves the build number to 30.2.A.1.21 for single SIM variants and 30.2.B.1.21 for the dual SIM variants. The latest update includes 1 September 2016 Google security patches as well as providing a fix for some users who had problems using their micro SD card following the Marshmallow update. The update can be downloaded via Xperia Companion, or the FTF firmware files are available below.
DOWNLOAD Xperia M5 FTF Firmware Files – Android 6.0
Xperia M5 (E5603) 30.2.A.1.21 Russia Generic
Xperia M5 (E5606) 30.2.A.1.21 Latin America Generic
Xperia M5 (E5653) 30.2.A.1.2 Australia Generic
Xperia M5 Dual (E5633) 30.2.B.1.21 Middle East and Africa Generic
Xperia M5 Dual (E5643) 30.2.B.1.21 Brazil Generic
Xperia M5 Dual (E5663) 30.2.B.1.21 India Generic
Thanks George, Hendr0, Jenge, Mice, Nicolás and Parag!