missing emails

hello,

I have been with videotron for many years now and with no issues.  Recently, I noticed that email older than 6 months are all missing in my inbox.  My email client is Zimbra on mac and I have multiple accounts. none of my other accounts has this issue.  I don't know what happened.  Was wondering if videotron support can verify logs to see what happened to those emails, or if anyone has any ideas what may have happened.  On the mobile, i use iphone mail.