If you find that emails are received without their attachments, the problem could be that your server has PHP's Safe Mode on. This needs to be turned off for attachments to work.
If preview emails do arrive with attachments but scheduled campaigns and autoresponders don't, this usually means that the command-line (CLI) version of PHP has Safe Mode on, even if the web version of PHP doesn't have it on.
The CLI version (the one that runs cron jobs) and web server version (the ones that runs IEM in your web browser) can each have their own independent settings. You need to turn off Safe Mode in both versions for your attachments to work. You may need to contact your host to do this.
