How to show the size of messages?

[test]

On Saturday, January 25, 2020 7:34:20 PM CET Ingo Klöcker wrote:
> On Samstag, 25. Januar 2020 18:42:42 CET test wrote:
> > On Saturday, January 25, 2020 2:45:08 PM CET Erik Quaeghebeur wrote:
> > > > how can I show the size of messages in the message list?
> 
> Did you try right-clicking on the column header of the message list? When I
> do this, then I get a menu where I can select all kinds of message
> properties (including size) to show. I'm using the "Standard Mailing List"
> aggregation with the "Classic" theme.

Ah I see what you mean!  I'm using "Activity by Date, Threaded" for 
Aggregation and the "Smart" theme.  Thus I don't have a header of the message 
and was clicking on the subjects of messages trying to figure out what you 
mean.

Using this aggregation and theme, how can I see the message size?  It would 
fit nicely into the line with the sender address and the date.