You can either right click on any attachment in an email and select “Save all attachments” which will save all the attachments in the email in one go.
Or as @Gary advised in the following thread post, if you have a Paid Pro or Personal version, you can also click “Attachments” at the bottom left of eM Client to see all the email attachments in one big list.
You can then save all the incoming and outgoing mail attachments “in one go” from any selection of email attachments from each account.
You can also narrow down the attachments per file-type, date, size, sender etc