I would like to make a static copy of the emClient database.
You could either close eM Client and then “make a copy of the hidden database folder” as per @Gary advised above.
(Hidden database folder Windows)
C:\Users\username\AppData\Roaming\eM Client
(Hidden database folder Mac)
/Users/User Name/Library/Application Support/eM Client
If you then remove any email from your current eM Client, you can do a partial restore “from a previous eM Client backup.zip file”. or do a partial restore “from a previous hidden mail database folder”. See my post in the following thread on partial backup restores.
Also see the following eM Client support page on restoring a backup including restoring a partial backup “part way down the support page blog".
Or if you have V10 you can also create an external hard disk (.emdf) file in eg: “Documents / eM Client” which “shows under the accounts on the left above local folders”, and create whatever mail acct folders you like under the data file to store any current or old account email.
The data file can then either be “left open / mounted permanently to update / add any mail to it”, or can be “unmounted / closed if you don’t need it open all the time” like archived or old account mail. This is similar to an Outlook pst / .ost file.
See the below eM Client help below on data files.
https://www.emclient.com/webdocumentation/en/10.0/emclient/default.htm#Data%20Files/Data%20Files.htm