There are various reasons your post might be rejected …
Wrong list address
Early in 2019 we moved the mailing list server to a cloud hosted virtual server. This necessitated changing the list addresses from ‘firstname.lastname@example.org’ to ‘email@example.com’.
For a while we forwarded messages sent to the @midrange.com address, but on February 14th those forwards were discontinued.
Please make sure your address books have the correct address.
Also, before resending your message, take a moment to make sure the correct ‘@lists.midrange.com’ address was not CC’ed on the message (to avoid duplicates).
To prevent bogging down the mailing list server, we limit the size of messages posted to the lists to 40k. Messages that are larger than 40k will generally be rejected.
If you want to post a large code fragment, consider using the midrange.com code paste service at https://code.midrange.com.