Was it a windows update? If it was there is now way to disable those updates. where did the updates come from. I have seen that Microsoft updates will remove any software that has not been approved by them. WIndows 10 home is good for this
There is no setting to disable checking for updates. When you are prompted, just decline the update. There are not that many, so it is not like a weekly.
eM Client does not delete data when updating. One possibility is when updating from version 6 to 7, you will be asked if you want to import the database. If you choose not to, then your data will not be there. You can import it at a later time by going to Menu > File > Import > eM Client 6. Otherwise updating from any version 7.1 to another 7.1 version will not delete your data.
It is always a good idea to backup before updating software; that is just common sense.
If you are not satisfied with eM Client, which seems to be the case from your comments on this forum, it might be better for you to look at other clients. It may be difficult to find one that does everything you want, so some compromise may still be needed.