Message says "email will be downloaded in next connection"

Looking for an alternative to Thunderbird an Outlook, I installed eM client v6 on windows 10 this morning. It looks promising so far, but I’m VERY annoyed when I click on an email title, and it displays a message “email will be downloaded in the next connection”.
How do I get to download all emails and attachments at once? Not found anything in the parameters that I re-read 10 times.
Thanks for your help.