https://forum.emclient.com/emclient/topics/sent-emails-not-stored-in-sent-folder
"I have 2 accounts that are hosted by a very large Canadian ISP provider Shaw using Zimbra as an email server. The accounts are set up with IMAP, SMTP and Airsync. These accounts were working perfectly for a couple of months and then the email stop being copied into the sent folder. "
Seems somebody manage to get airsync/activesync working with zimbra before.