Microsoft Azure

mail_location = obox:%u:INDEX=~/:CONTROL=~/
plugin
{
# Old?
# obox_fs = fscache:1G:/var/cache/mails:azure:ACCESSKEY https://STORAGENAME.blob.core.windows.net/

# Newer (verified January 2018)
obox_fs: fscache:1G:/var/cache/mails:compress:gz:6:azure:ACCESSKEY https://OBJECT_USER.blob.core.windows.net/CONTAINER_NAME/
obox_index_fs: compress:gz:6:azure:ACESSKEY https://OBJECT_USER.blob.core.windows.net/CONTAINER_NAME/
fts_dovecot_fs: fts-cache:fscache:1G:/var/cache/fts:compress:gz:6:azure:ACCESSKEY https://OBJECT_USER.blob.core.windows.net/CONTAINER_NAME/
}

Get ACCESSKEY and STORAGENAME from www.windowsazure.com -> Storage (-> Create STORAGENAME) -> STORAGENAME -> Manage Keys.

Given current obox code (January 2018), storage account is required to be General-purpose v2. (Blob storage account will not work.)