[OSM-talk] weird "excessive bounces" warnings from the list

[Richard]

Hi,

from time to time I am getting messages like 

<<Your membership in the mailing list talk has been disabled due to
excessive bounces The last bounce received from you was dated
30-Sep-2018. ....>>

Any idea.. what could be the cause? Unfortunately I don't see any way
to figure out which message did cause this.
I notice the first message I did not receive was 
  https://lists.openstreetmap.org/pipermail/talk/2018-September/081459.html
but is this the "offending" message?

The messages go straight into a dedicated gmail inbox without any 
filters.
As far as I know gmail will only ever reject messages that contain
what looks to it like executable programs - attached files 
(*.exe, *.com, *.bat)

Richard