Post by email – Forwarded email stopped working

For the last couple of months users have been able to post content via <obscure_username>@mydomain.org.uk as I have set up a mail forward from this address to the <random_username>@post.wordpress.com address configured within Jetpack.

This week this has stopped working. My email forwarding is working OK, no bounce messages have been received but sending directly to <random_username>@post.wordpress.com does still work.

Has something changed with the post.wordpress.com email handler such that it is now rejecting email not sent directly?

Anyone else having this problem?