How to configure maximum IMAP connections in Mac OS X Server (El Capitan)

emailimaposx-serverserver.app

In previous Mac OS X versions (to El Capitan), you could administrate mail server settings in the app called Server Admin. In El Capitan, all I have access to is the Server.app. In there are only very limited settings for the email server.

We are now in the process of leaving this in-house email server for Office365 and Exchange. In order to migrate all user emails from our server to the cloud servers in Exchange, we need to increase the maximum number of IMAP connections allowed.

I can't seem to find where to do this? Server Admin could do this but that won't work in El Capitan. Any ideas?

Best Answer

You should be able to increase the number directly in the respective config file:

  • Stop the server:

    sudo serveradmin stop mail

  • Modify the file /Library/Server/Mail/Config/dovecot/conf.d/20-imap.conf and increase the number of mail_max_userip_connections right at the end of the file:

    ...
protocol imap {
  # Space separated list of plugins to load (default is global mail_plugins).
  # stats (in global mail_plugins) and imap_stats (here) are also available
  mail_plugins = $mail_plugins imap_acl imap_quota imap_zlib

  # Maximum number of IMAP connections allowed for a user from each IP address.
  # NOTE: The username is compared case-sensitively.
  mail_max_userip_connections = 20
}

  • Start the server:

    sudo serveradmin start mail

Other (Linux) sources recommend to add a similar entry in the global section of the same file or in /Library/Server/Mail/Config/dovecot/dovecot.conf.

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