After you set up your Gmail account you might encounter this error message:

'All Mail' folder disabled

For Gmail and Google Apps accounts, eM Client synchronizes the 'All Mail' folder. It appears that IMAP access for this folder on account '<your email address>' is currently disabled and synchronization will fail.

To fix this, you need to make sure the 'All Mail' folder has 'Show in IMAP' checked in their Gmail settings at https://mail.google.com/mail/u/0/#settings/labels.

Simply follow the directions from the error message and enable All Mail label to be shown in IMAP.

NOTE: The 'All Mail' folder is a vital part of your Gmail account - it stores all the messages in your account (with the exception of Trash and Spam folders - these are separate).
Synchronizing this folder will not create any duplicates of your messages, because eM Client supports this specific Gmail structure and each message is stored only once in the All Mail folder and all the other folders (Inbox, Sent, Drafts, ...) are just Labels - special search folders which will show the messages from All Mail folder with the matching Label. Kind of like Tags in eM Client.

This actually allows for the synchronization to be faster and the data to take up less space on your device than if the Labels were converted into real folders.