On Edit: SmarterTools has provided me with a pre-release upgrade that seems to have resolved both issues. You will still need to follow my guide to add the ClamSup signatures to the freshclam.conf file, but they won't be overwritten by re-install or upgrade. We just need to get a few minor things going with SM 14 and it will be the best SMTP client out there. ST is communicating with me better and I appreciate that. Please wait until the next minor release (should be on 06/16/2015) before upgrading.
Then add my ClamSup thread files to the freshclam.conf and you're good to go.
The CalDAV issues with iOS devices seem to have been resolved.
Thank you SmarterTools. I hope we can work closer together Tim. I have many good ideas and I think I've passed on more than my share to date. I hope you agree.
END of EDIT.
I'd recommend against upgrading to the latest 13.x or 14.x SmarterMail.
SM 14.x has SERIOUS CalDAV problems with iOS devices.
SM 14 has SERIOUS problems with ClamSup.
I cannot get SmarterTools to open a useful conversation with me despite them asking me to be a Product Expert. Very frustrating. I honestly don't think they even understand the problems. I could help but I have no way to do so.
Do yourself a favor. If you're on a stable version do NOT upgrade at this time. It will only aggravate you and severely piss off your customers or users
These problems should be resolved in a matter of minutes or hours.... not days, weeks or months.