when filter, use /SpamAssassin and the like to fight spam.
Using mutt with Gmail's POP service
Currently, running mutt with Gmail's POP service doesn't work well when
mutt is only used to browse remote mail: users will not always see all
the messages in a folder.
To fix this, you must login to Gmail from the web interface and go
'Settings' -> 'Forwarding and POP' -> 'POP Downloads' and select
"Enable POP for all mail (even mail that's already been downloaded)".
You might also want to change the "When messages are accessed with POP"
option according to your needs.
When working with POP folders, mutt can cache headers as well as whole
messages to reduce the download time greatly, see
/Caching for details.