1. he receive appointment invitation,
   
2. that event was created by outlook/exchange,
3. and that event is recurring (e.g. every week)
4. he accepts the even in Zoho calendar
5. In zoho > he sees only the first occurence (the rest is gone).

I am not able to verify his complaint since I don't use MS products.

I did a test from a gmail account, and it Zoho imported to occurence correctly.

Do you know of problem with recurring event invitations sent by Outlook users?