You are comparing apple with oranges.
Yamm and Gmass will imitate you sending out email from Gmail via API.
They violate all anti-spamming rules as not disclosing the fact, that you ARE bulk sending and not giving list-unsubscribe option. (Opposite of bulk sending is hand-sending, and you don’t need Mautic for that) By faking your sending method you can not scale above 500 emails / day. If you try, Gmail will punish you. If you will keep sending your 500/day, and Gmail notices, that you fake the ‘bulk’ setting in your header, they will punish you, and never get to inbox again.
SUMMARY -> You are Spamming, and it is NOT SCALABLE
Mautic will send an email by using your Gmail SMTP creds using LEGIT bulk mailing technique (Precedence: Bulk, list unsubscribe). If you hqave the bulk tag, you’ll be judged differently. Your emails will land in Promo (Which you are actually, so nothing wrong there) and if you have a relationship, good engagement with these customers, you’ll land in Inbox very soon. Try to make them answer you an email, and it will work.
SUMMARY - > You are conducting legit business, SCALABLE
As you can see I’m always trying to convince you to do the right thing, and not try to fake anything. You put way to much effort into testing and forcing your way around the Gmail AI. It won’t work. No matter how slow you are sending, how you tweak your content, or even if you fake your identity. You can fool the algorythm for a while, but you’ll be cought very soon.
I’m also not a fan of the titles you are using (but I’m nobody here, so whatever), because it’s not Mautic who is landing in Spam, but your content.