Every platform has issues. I'm looking in my Spam folder now and see emails from lists I subscribed too sent via Infusionsoft, SMTP.com, NRAmedia.org (I've been an NRA member for years and their email still goes to spam), Vertical Response from Jay Baer (I interviewed him on my podcast), email.imodules.com (from one of my Alma Maters, Texas A&M), jupiter.salesmango.com (I did subscribe to their list), serv01.c8518.sgvps.net (for a program I did enroll in), icontactmail2.com (for a list I did subscribe to), multi197.postfix.bmsend.com (I didn't subscribe to this), socedo-2.mail.intercom.io (I signed up for this.)
Dang...now I have to go make a blog post on this!
Hotmail, Yahoo, AOL, and MSN are the biggest culprits for me when sending with Infusionsoft and they always have been, with gmail close behind. I have the same issue when sending to those domains with HubSpot.
For 7 years I've asked for a straight answer on deliverability and it's a more closely guarded secret than why Hillary wiped 30,000 emails pertaining to yoga routines and Chelsea's wedding.