Hi Wayne,
Thank you for the reply.
I tried with default featured image plugin. But then, it will show a single image for all posts even if I attach an image in email which is meant for featured one. Hence I removed the default featured image plugin.
I tried attaching an image named a.jpg for all posts that doesn’t contain any other images. But in that case, the media folder was creating a-1.jpg, a-2.jpg etc. for every posts.
So no workaround yet.
It will be nice, if I can set a default featured image in Postie settings itself, when there are no images attached in a mail.