Dear Sogo user, I have the same problem and I think I found the solution after long investiagions. Our email server is separated from the Sogo-server and I found out
that the Sogo server has permanent ProxyTimeout errors. The reason for that ProxyTimeout errors was, that the (Outlook 2016) avtiveSync client is checking every file on the email storage. Unfortunately we have the emails stored in the same folder like out Windows user profiles. This profiles are quite huge and the Sogo-server search in every user profile folder and subfolder for valid mbox files. This means the Sogo-server checks every file header for every file in the user folders and creates the error message that these files are not valid mbox files. The email folders are used very often parallel with IMAP Clients like Thunderbird that are using a .subscription file for email folder subscription definition, but activeSync or the Sogo-server does not interpret this .subscription file. For me is not really clear if the Sogo-server or email server searches in all existing files and subfolders for a valid mbox file or is this cause by the activeSync protokoll. You can public my solution, but without my sender email address. Kind regards CGB -- users@sogo.nu https://inverse.ca/sogo/lists
