Almost all spam I receive is from Gmail. It's gotten so bad I've actually setup a filter that routes everything from @gmail.com into spam - except for some whitelisted email addresses. G Suite is fine, it's only @gmail.com that is an issue

And yes, it's genuinely from Gmail; valid SPF, valid DKIM, came from a Google IP address, etc...

To say the biggest source is Gmail might be technically wrong though - I suspect there's a large volume of spam that Migadu (my provider) is dropping before it even reaches my inbox, i.e. emails that it is 100% sure are spam and it can just drop. Nevertheless, an overwhelming amount of spam I observe/have to deal with is coming from Gmail. Second to that is outlook/hotmail.

> To say the biggest source is Gmail might be technically wrong though - I suspect there's a large volume of spam that Migadu (my provider) is dropping before it even reaches my inbox, i.e. emails that it is 100% sure are spam and it can just drop. Nevertheless, an overwhelming amount of spam I observe/have to deal with is coming from Gmail. Second to that is outlook/hotmail.

This. It's more likely to be survivorship bias -- the gmail emails happen to survive because gmail is more trusted.

Re: [citation needed];

> Gmail obvious spam still #1 in the quarantine folders..

-- Michael Peddemors, President/CEO LinuxMagic Inc.

https://www.mail-archive.com/[email protected]/msg14526.html

The citation you are looking for is my inbox. That's the spam that still makes it through and there is quite a bit of it, conversely some ham consistently gets misclassified as spam or just simply disappears entirely.

You are of course welcome to not believe me.

I will echo this experience. An example of an email that made it through from a gmail.com account (abbreviated, it also contained links to some apps (the main purpose I assume) and much more text):

شهر مجاني عند الاشتراك السنوي $ الأسئلة الشائعة

    In 1979, LA residents were wearing masks — because of smog Los Angeles Times staff photographer Boris Yaro photographed Sera Segal-Alsberg on Crescent Heights Boulevard in West Hollywood Segal-Alsberg, an artist-instructor, was en route to teach a class at the Los Angeles County Museum of Art
    للمزيد من الأسئلة

    — In another sign of live entertainment’s rebirth, Bruce Springsteen returned to Broadway over the weekend
    يقوم الموظفين بتسجيل حضورهم ، انصرافهم الشركات العصرية مع الاستفادة القصوى من الإمكانيات الهائلة التي تقدمها لنا تكنولوجيا العصر أو الهاتف المتحرك ( الجوال ) أو إذا كنت تستخدم الحاسب فيمكنك استخدام أو يمكن للإداري تحميل هذا التطبيق على جهاز تابلت اشترك في النظام 10

    Diverse yet divided cities
    واحد أو عدة أجهزة ثم يضعها اشترك في النظام تسجيل دخول فقط في الأفرع المسموح له بالتبصيم فيها  |  أسبوعين كما أن الموظف لديك يستطيع التبصيم في ثوان قليلة بريد إلكتروني هو نظام إلكتروني قوي وحديث يستخدم لتسجيل فهل يمكن استخدام النظام في جميع هذه الأفرع أدخل بيانات الأفرع إن وجدت الموظفين

    Experts say the Delta variant poses a greater chance of infection for unvaccinated people if they are exposed The variant, first identified in India, may be twice as transmissible as the conventional coronavirus strains It has been responsible for the rise in cases recently in India, the United Kingdom and elsewhere
    في مداخل الشركة أو أفرعها المختلفة يمكنك الاعتماد على أي جهاز إلكتورني حديث أو حتى قديم في تسجيل ومتابعة تبصيمات الموظفين ، إعرف المزيد اشترك في النظام مجانا , أدخل بيانات الشركة والموظفين

When I ran my own mail server some years ago I was shocked at the amount of spam originating from Google. Definitely their IP addresses as I would routinely get other legitimite mail from the same IP ranges. Was quite a challenge dealing with these spam as it wasn't as simple as blocking their ip ranges as the vast majority of my personal contacts use Google. Never saw the same from Microsoft, Apple, etc.