Download all headers but no body?

[beaky]

I receive a steady trickle of spam. Some is obvious, so goes straight to deleted, but others can only be spotted by reading the headers.
Using IMAP, are "all" the headers downloaded to the local device? Including all the routing ones "Received:" etc? Or is it just the to, from, subject and date?
Are they only fully downloaded for messages for which the message body is downloaded?
I cannot find a way to view the full headers (necessary to look for evidence of spam) without opening the message content. Opening spam is not a good plan!
Have I missed something?

[Kostya Vasilyev]

>> Using IMAP, are "all" the headers downloaded to the local device

No, just the ones the app needs.

>> I cannot find a way to view the full headers

Select exactly one, not more, not less, message in a message list -> Menu -> Show headers.

[beaky]

Thanks.
The trick I had not spotted was to tap on the coloured square, to select,but not to open.
Works a treat.

[Kostya Vasilyev]

Or you can long press a message to toggle its selection state on/off.