Mutt error ‘/home/user/mail/ is not a mailbox’, but configured for use with gmail imap/smtp

I have successfully configured mutt to work with gmail imap.
But when i try to send mail via gmail smtp, i get this error:

/home/user/Mail/ is not a mailbox

I cannot understand why /home/user/Mail plays a role when i am not trying to send mail to a local unix user. This should only be relevant if i tried to send mail to a local unix user, and somehow whatever is inside /home/user/Mail/ is not a valid mbox

The error just makes no sense to me, and i do not know how i can get rid of it so i can finally use mutt to do my everyday email -tasks using gmail´s smtp service.

The config looks like this:

set from            = "gmail_user@gmail.com"
set folder          = "imaps://gmail_user@imap.gmail.com"
set smtp_url        = "smtps://gmail_user@smtp.gmail.com"
#set imap_pass       = "PASSWORD"
#set smtp_pass       = "PASSWORD"

set my_spoolfile    = "INBOX"
set my_mbox         = "Archieves"
set my_record       = "Sent"
set my_postponed    = "Drafts"
set my_spam         = "Junk"