Campaign Emails landing in clients' spam/junk folder

Over the past few weeks, my sales have dropped off a lot. I start going back into client’s campaign of those I knew would purchase based on our conversation and I’ve noticed my sales campaigns emails all of sudden are not getting opened after reaching out to 10+ clients my emails are landing in their spam/junk email box.

This campaign I’ve been using for 2+ years and has worked fine, what has changed to cause this, I’m not doing anything different?
Help as this is causing me to lose income.

Check this out: Email Authentication with SPF, DKIM and DMARC - Meppy

And another worthwhile guide: The Ultimate Guide to Infusionsoft Email Deliverability - WeDeliver.Email