Thanks Stephen and Mark.
I checked whether group and world have 'x' permission on every directory in the path to the files and found below:
root@lists:/var/lib/mailman3/templates# ll total 12 drwxr-xr-x 3 list list 4096 Oct 10 2018 ./ drwxr-xr-x 12 list list 4096 Jan 9 05:08 ../ drwxr--r-- 5 list list 4096 Mar 30 2021 lists/
root@lists:/var/lib/mailman3/templates# cd lists/ root@lists:/var/lib/mailman3/templates/lists# ll total 20 drwxr--r-- 5 list list 4096 Mar 30 2021 ./ drwxr-xr-x 3 list list 4096 Oct 10 2018 ../ drwxr--r-- 3 list list 4096 Jan 8 01:14 [redacted].lists.[redacted].org.au/
root@lists:/var/lib/mailman3/templates/lists# cd p[redacted].lists.[redacted].org.au/ root@lists:/var/lib/mailman3/templates/lists/[redacted].lists.[redacted].org.au# ll total 12 drwxr--r-- 3 list list 4096 Jan 8 01:14 ./ drwxr--r-- 5 list list 4096 Mar 30 2021 ../ drwxr--r-- 2 list list 4096 Jan 15 04:45 en/
So, group and world did not have 'x' permission to all the superordinate directories.
I didn't see anything relevant in mailman.log.
I am not sure why the "list:user:notice:welcome" and "list:user:notice:welcome.txt" has different sizes even though they contain the identical welcome message.
I decided to delete these two files: list:member:regular:footer list:user:notice:welcome
Restarted services and tested again. -> issue still persisted.
Should I try giving group and world the 'x' permission for all superordinate directories? Although my other mailing list has the same setup (no 'x' permission for group and world and it seems to be working fine.)
Thanks for your help.
Frances