Actually, there was no issue with the workflow or properties.
The ‘Inbox’ folder is segregated into ‘Primary’, ‘Updates’ and ‘Promotions’.
I was considering only ‘Primary’ section. But there are other 2 sections as well. And those sections are also getting updated with new mails. The mails which I was interested is present only in ‘Primary’. But still all the sections are considered so I had to increase number of mails count to be iterated