[npsomaratna]

To add my two cents: my company had the same problem - despite checking all the boxes ourselves.

When testing, something we noticed was that the content of our emails/newsletters had a significant impact on whether they ended up in the inbox vs. spam.

Of the major service providers, Outlook seems to put huge importance on the content of the email. The simple addition or deletion of a couple of words can dramatically affect spam rates.

Yahoo is less trigger-happy about content; and Gmail least of all. However, even for domains with a good sender reputation, Gmail will spam emails if the content is too 'spammy'.

Shameless plug here: we ended up building a tool to test out various email subjects/bodies against the big 3 providers above (you can even plug in your own email address/service when testing). Do try it out - I'm sure you'll find the results eye-opening: https://vetter.monsoonyeti.com/